I agree with paying half. You are being more fair than a lot of people would. Both of your names were on the account so I doubt she will be able to take any action against you. (however, like Joe, I'm no judge...but I did sleep on my couch last night. )

Just make sure that if you do pay her have make it traceable. Pay her with a check and have her sign something saying that you paid her. I'm seen to many Judge Judy shows to know not to ever have proof.