if she doesn't pay it you have to. but, you can take her to court and sue. may not sound like a great idea since you are family but if you don't, and she refuses to pay, you will have to make all of the payments leaving you SOL. she needs to learn this is part of life and when you have responsibilities you can't just walk away because you just don't want to pay for it anymore. to be fair, sit her down and tell her what you are going to do if she doesn't pay the loan and that it will not only effect your credit but hers as well. also let her know, if it's on her credit, good luck finding a decent apartment or buying a house until it's resolved.