Workingman,
I have a few lifestyle type questions about your girlfriend:
Is she a smoker?
Does she take birth control?
Does she consume enough water?
Being sexually active as well as certain lifestyles can alter the delicate balance of the female anatomy. As a nutritionist I generally recommend taking a daily multivitamin like Lavada or something similar to help maintain her intimate environment.
I would also talk to her outside of the bedroom about your concern. Sometimes these situations bring couples closer together. The good thing is that this is a common problem with women and she can get through this fairly easily.