So... I had her show up, say "Hey, I know awesome magick, would you like to know awesome magick?"

I agreed, she said "AWESOME, lemme just leave my signature and OOP MY TIME HERE IS UP PEACE."

I'd like to know how to actually get magicks from her.

@xxizzypop: Leave the area. When you come back, you should see her summon mark on the ground, before the water.

You have to summon her again. So you need to become human and head back toward that lake where you (I assume) defeated the Hydra. If you look around you should see a summon sign for her. She will then sell you magic for souls as per usual.

@Rayeth: When she said she was leaving her signature, I assumed I had to be human, but, that's good to know for sure. Thank you. Are the spells she sells worth much?

Edit: As in, are they meaningful or just a waste of souls?

I summoned her and one of those crystal golems killed her. Dammit.

While in human form, go to where the hydra was and you can see her summon sign.

Also, after you have summoned her, reload the game/area. Then go back to where you freed her, you'll find something.