A library card probably isn't too hard to acquire. You just need a utility bill and some kind of photo ID. You could come up with something that would work. Then just check them all out again under a fake name. How many books did you have checked out? And how overdue were they? Were they even worth $85?
If you want revenge against the librarian, I don't see how stealing the books back even affects her. She's not going to care if the books are missing so you're only depriving other visitors in the library access to the books. Also, it's your own fault that they were late. Everyone knows that there are fines for overdue books and that if you don't return them on time, you pay the fines. In a way, your $85 is helping to pay for your local library, which has given you free access to books your entire life. Not that I'm trying to pretend that I have morals, but I'm just sayin...