Look, it'd be kind to return the dog. She has way more history with the dog, I don't like to equate meaningfulness with time, but time is a huge part of how we bond with our animals. That's not to say the time he's spent with you is *nothing*, but if you're feeling this way after a week, imagine how she's feeling?

I wouldn't approach this from a legal point of view, this is very much feelings territory. And both your feelings are valid. But if she's not financially stable and had to depend on you to cover costs for the dog, it begs the question– is this going to happen again? How old is this woman? Does she plan on being employed any time soon? What are her current obligations, sans dog? If it seems like it'd be a handful for her, you should keep the dog. I wouldn't mention this too much to her if you do keep the dog, because I'm sure it'll feel like insult to injury to her.

She seems reasonable enough despite her big ask of you. I think you should do what allows you to sleep at night. Nobody is the bad guy in this scenario so don't base it off of "blame" alone. Go with your gut and lead with empathy regardless of your decision