Can I refuse to give my friend the answers because she won't give me the textbook?
What are you going to do instead?
I'm going to give her some time to think about how to retake the tests.
Even though you should help your friends, it is her responsibility to be prepared for class. She cannot depend on other people all the time.
She won't be able to do it without the answers.
It sounds like you are doing her a favor here by not helping her, and hopefully she will be able to learn the answers on her own with enough time.