She doesn't masturbate? Then how does she know what she likes in bed? How can she possibly direct you in pleasuring her so that she gets the most out of your intimate experiences? If she doesn't know what she likes or how she likes to be touched then intimacy may be an issue for you down the line.
Also, all men masturbate. Men are visual creatures and they look at porn to facilitate arousal during masturbation, whereas women's fantasies tend to be more mental. Masturbation is a natural, healthy thing. If your girlfriend has hang-ups about this, well, you may need to try to have a serious talk with her about this sort of thing.
It would probably be a good idea to make sure that you have total privacy before your next masturbation session