Gosh, such an awful situation. Is she really a friend or someone who is using you from time to time. I would consider saying au revoir (goodbye) to her and keeping the kitty.

It sounds to me that if she did get a new cat, she would again, when convenient for her needs, ask you again, to take care of one of her pets.

She would not be a friend of mine for very long. She sounds like she needs some counselling first, then maybe a good job and a place to live. Pets are way down there on the list of things she needs right now.

Stick to your guns, keep the kitty and tell her to go fish.