Dog drama, help me out

My family was asked to foster a dog for a few months. (To me that meant 3-4 months) We have soft spots for animals so we didn't even think, we offered our help. We were told the girl was going through a break up and went back to her parents where and the dog was not allowed.

It has now been 6 months, she has only visited once. All other visits, she bailed and never came. She does venmo money for food, and that’s it. When the dog went in heat it was huge mess, but we knew going into it that she wasn’t fixed. We provided all doggy diapers and took care of it.
We’ve told her repeatedly that the dog may have an ear infection (we took her to the vet and never told the owner just to see if she cared)
Meanwhile, dog owner is on social media showing off her new nails, clothes, hair etc.
I’m sure you’ve figured out my question… would I be an asshole if I tried to keep the dog? With all that I’ve stated is it fair? My family is very attached to her and don’t want to give her back. We also cringe at the thought of this sweet dog going back to her and being pinned in a too small crate 8-10 hours a day. She’s had free roam in my house since day one and never a problem.
What do you all think?

Just ask her. I bet she does not want the dog. Provide her will the bills that you have invited for the dog and tell her she can pay them or you will accept the amount as a re-homing fee for you to keep the dog. Tell her you understand that now is not a good time for her to be a dog parent and you will take it over from here or she needs to pick up the dog immediately. She won’t! She will leave it and probably agree. And you will have text evidence of the re-homing agreement. Yeah I never take animals here cause we will want to keep them and animals are very hard to re-home unless full blooded breeds.
Good luck