I know that Quelana in Blightown is supposed to give you this spell, but I have no idea how to get it from her. The Dark Souls wiki states this, "Quelana gives it to you after finishing her favor." She has never asked me to do anything for her. Any help?

I think you need a specific starter item to even get her to talk to you. I just killed her for the fire keeper soul.

You have to kill the bed of chaos boss and return to her.

You might need to buy all her pyromanceries first, probably should.

She didn't ask me either, but I knew the favour was kill the bed of chaos, so I crossed my fingers and did it anways after buying out her inventory. It worked out and the 'get all pyromancies' achievement popped when I returned to her.

@Stahlbrand: Excellent. Thanks.

I njust finished the game and I had no idea anyone called Quelana existed... and I explored everything thoroughly