I just started reading The Last Wish. It's a great introduction into the character. It's mostly short stories loosely tied together as chapters rather than a novel.
Sword of Destiny I guess was published first but it takes place after The Last Wish, and is more short stories. It's also kind of hard to find an english translation at the moment, I guess a new edition is coming out this December.
And then you have all of the novels starting with Blood of Elves.
But The Last Wish is reeeeeaaaallly good so far. I've never had to look up so many words while reading a book, and it's awesome.
I never used her. You get better healers eventually.
I never finished that game because I'd constantly restart battles when I'd lose characters, so I encourage you to just keep trucking. You're also pretty early on so you'd probably be okay with restarting if it eats you up inside. You monster.