There are variables that can not be answered with just the stated facts above.
First off, Student loans are typically non-dischargable in bankruptcy. If she managed to receive a discharge for some rare reason, the ruling on that discharge may bar you from seeking to collect for that debt.
However, if she does not receive a discharge on the student loan, depending on the circumstances of you agreeing to be a cosigner, including provable facts, documentation etc. it may be possible to prevail in a suit.
Again with the limited information, I could not advise you one way or another. I would strongly recomend speaking with a lawyer in your area. Make sure you discuss the circumstances and any agreement concerning you being a cosigner with that lawyer. and make sure you have any information concerning her bankruptcy discharge, particularly anything to do with a determination as to dischargability of the student loan.
Good luck to you
This response is for general information purpose only and does not create a client/attorney relationship. The answer is not complete and may not be the best course of action for you to take based on the limited information. You are encourage to seek at least a consultation with an attorney to see your options on the matter.