This really sucks, I'm trying to stay more offensive and get right up in her grill (as most attacks miss this way) but I'm doing such little damage that it's unrealistic in killing her.

I'm guessing using fire isn't a good idea.......sigh...I'm finally at a "choke" in the game and I'm debating going ALLLLLL the way back to firelink shrine to do some of my upgrades, etc.

Sad thing is, is that I don't even think I can make it all the way back.

Also, I know I can request to be "summoned" into another players world, but can I summon a player into mine to help me fight this boss? I wasn't sure how that goes exactly...

Step 1: Go Human form.

Step 2: Walk towards her cave from the bonfire

Step 3: Get invaded

Step 4: Kill NPC invader

Step 5: Summon NPC invader at boss fight

Step 6: ???

Step 7: Profit

I'm not sure what boss you're talking about.  Do you mean Queelag?  The lava-spider-lady thing?
 
If it is Queelag you're having a hard time with, then I suggest you get some help, as I had quite a bit of trouble with her as well.  You can only summon phantoms into your world while you are in human form (if the number next to your health/stamina bar is white, you're human--if grey, you're hollowed), so you'll have to have some humanity.  If you turn human again at the bonfire nearest Queelag, then you will be invaded by Maneater Mildred.  If you kill her, then you will be able to summon her to help you before entering the boss fight.
 
An easy way to kill Mildred is to run away towards Queelag's Domain.  Once inside, Mildred cannot exit Blighttown and therefore cannot follow you, though she will keep trying.  Feel free to pelt her with arrows, bolts, sorceries, or pyromancies with complete impunity.  Once she's dead you'll get some souls and her big ass knife weapon.  Then you can go ahead and summon her near the boss arena entrance.
 
You could also, of course summon another player, but there simply might not be any putting soul signs down in the area.

@eastcoasteric said:

Also, I know I can request to be "summoned" into another players world, but can I summon a player into mine to help me fight this boss? I wasn't sure how that goes exactly...

You have to be in human form to Summon other people. As for the boss, sorry to say I can't help much. Playing a Sorcerer lava management seems to be the biggest concern since it can lead to the end of you fairly quickly.

Circle her with you shield while dodging the lava she spits out, attack when she misses an attack, repeat. It's not that hard dude.

I pretty much used your strategy of staying in its face. The fight took forever, but I didn't run into too much trouble. By staying between the crevice made by the bug half's head and arm, I took no damage from 90 - 95% of the melee swings. The only other thing I had to watch out for was the human half going limp, which means to get back because an explosion's incoming.

Wish I would have known there are NPC invaders, though. After reading some of the previous responses, I assume kindling or reverse hollowing turns me human? I figured it was linked to my humanity score, and I just died too much to get anywhere near human. Highest humanity I've had was three or four.

I pretty much used your strategy of staying in its face. The fight took forever, but I didn't run into too much trouble. By staying between the crevice made by the bug half's head and arm, I took no damage from 90 - 95% of the melee swings. The only other thing I had to watch out for was the human half going limp, which means to get back because an explosion's incoming.

Wish I would have known there are NPC invaders, though. After reading some of the previous responses, I assume kindling or reverse hollowing turns me human? I figured it was linked to my humanity score, and I just died too much to get anywhere near human. Highest humanity I've had was three or four.

The only way I was able to beat her was by kindling the bonfire near it, and using flasks when the poison got my health too low. The only really safe time to attack her is when she does the long range lava attack, run in close and hit her sides once or twice, then immediately back away and wait until she does it again. Her up close attacks and explosions are too damaging to risk getting hit by. It does take a while, but eventually you will wear her down.

My best advice is to equip your best fire proof gear and attack from the side in between her attacks. Look out for when the lady part lies down on the spider because she is about to use her lethal AOE attack.

@eastcoasteric: You have to be in human form to summon a fellow player to help you out.

When you have a humanity (counter is on 1 or higher), go to a bonfire and select "Reverse Hollowing". This will make you human, and consume 1 humanity.

Then you can interact with the white scribbles on the floor to summon a friend. You can summon more than one, if you want to.

If you don't have humanity, the easiest way to get it is to get summoned yourself. Go towards the fog gate before the boss, put down a summoning sign somewhere right in front of it, and wait for a bit. You eventually get summoned by another player, and when you help him kill the boss, you get souls and humanity in return.

Helping other players is also a really good method to "practice" boss fights, seeing you can observe all the mechanics, see what other players do, and because you don't lose your souls when you die. Even better, you will respawn right back at the boss gate if you fail.

If you wanna go back to Firelink Shrine, take the water wheel right as you exit from the bonfire. Keep going up and it'll take you to the Valley of Drakes. From there, you can walk across the plank to New Londo and back to Firelink. You don't HAVE to truck through to the sewers to the aqueduct.

Thanks for all the helpful info everyone, I just had a chance to review through all of it and here is my situation...

First, with the "being" invaded by the NPC demon, this has already happened to me ( I honestly thought it was an actual character and I got super excited that I was FINALLY being invaded...and then my hopes were let down as I realized that it was just a NPC, that I disposed of insanely quickly.

So after that I had put a few summon signs down while human and waited, waited and nothing. (this thing where their servers are too empty is starting to get to me).

So I tried fighting the queen.

After a good 20 minutes, I had her health almost to about 35% when she used that "blast" thing that deals major damage from all sides of her.

And then died.

So I rushed back across the swamp (which is annoying because you get poisoned every time) and went back in hallow form.

This time in hallow form, I had my summon sign answered and hopped in another players game which was using the NPC summon you can catch from earlier and the NPC summon was quickly destroyed and I could not use any of my estus flask (I've yet to have this happen to me before, so I don't know why it did now) and of course, like clockwork and with no way to heal myself, I quickly found myself dead.

So it's note worthy to say that I have the best fire resistance equipment on and that I'm a pyromancer.

The weapon I'm using is only getting about 40 damage at a time, I have no idea why it's so low...it's getting very annoying.

I'm at a really bad stuck point right now and it's starting to get under my skin as I'm playing to the best of my ability but it's just not happening, I think a trip back to the firelink shrine to upgrade, etc is going to be needed. ugh

@eastcoasteric: I'm playing a thief, so I am able to move fast and dodge pretty much all her attacks. What I did was dodge all of her sword attacks, and only attacked her when the spider was spitting out lava, because this is her longest animation. I would circle her and attack her in the legs. It takes a while, but I found the boss to be pretty easy like this

@eastcoasteric: You cannot use Estus while you are summoned or invading. This part of the game. However, if you are summoned as a helper, whenever the guy who summoned you gulps on his Estus, you'll get some of that as health too - so it's pretty helpful. If you find yourself in need of healing as a phantom, consider getting the heal miracle.

Also, consider getting yourself a full set of thief clothes or the ninja outfit. Wear them as you hop from isle to isle across the poisonous water, occasionally killing the mosquitoes as they come. Hopefully you'll reach the entrance to the spider cave with all your Estus. Then swap out to fire resistant clothing - combination of hard leather, knight outfit and/or red robes might help. IIRC there's a set of red robes on top somewhere on the waterwheel construct, which you gotta cross a tiny beam of wood to get to. The robes also come with a sorcery that cures poison (!), and, surprisingly, is the only thing I've seen with curse resistance.

@White: Yeah I went through the entire area and picked it clean of all the items and I have the "ninja" outfit that is decently resistant to poison, but half of the time I'm in such a rush to get there and avoid the dudes with the massive boulders (though I have beaten them plenty of times before) that I just get poisoned, make my way to the queens liar and chill out at the bottom, leaving me 2 estus flask less than I had started (with 10).

Just after I wrote this I actually went into human form, called upon that Mildred or whatever chick and put up my best fight yet against this enemy.

I found it to be pretty easy and I would have ended up beating her if I had moved around a little more in the area (because the lava eventually surrounded me).

If it wasn't for the lava, I would have had her beat.

When I get back home tonight, I'll be likely to beat her, as long as I can re-summon Mildred again.

It's also notable that it was rather weird that when I was summoned as a phantom in someone else's game and they had Mildred fighting with them, that she died like 10 seconds into the match but with me she only had like 10% of her health taken away. (she took/blocked, most of the damage while I just got close to her front side and cut the crap out of this sexually confusing beast).

I shall report back later with a confirm kill and if you're on my server and see a "I DID IT!" sign in the middle of that area, you'll know it was me and I defeated this pain in the ass boss!