Squish, if it takes medications and drugs to make Chance feel good, or to give her more time--is that really what's 'right'? It means things can be done, thanks to modern science. But at best, it's a cheap imitation of a life she used to have.
I would, at any rate, recommend putting her down. She had a grand old run of it, and she is loved. You can do no more than just let her go with dignity, you know?

“There's a lot about discovering who you are and how difficult that is, and it never stops.”
- Libba Bray