What can I do to help my girlfriend with her back problems?

Only a doctor is going to be able to help your girlfriend - they will be able to make suggestions - braces, cortisone shots - to help her. In the meantime, I think you should limit the mage time. It isn't helping her and you are starting to resent the time you spend with no results. Please try to get her to go back to the doctor - or see a new one!