I had the same problem with the last girl I was with. Remember the scene in Talladega Nights when Will Ferrell is interviewed for the first time and he says he doesn't know what to do with his hands? I just kept thinking about that and I actually laughed a bit at the time. Annnyyywwwaaay, I suggest "helping" her do it a few times. Obviously don't tell her she's crap. Women hate that. Try making it part of the sex, perhaps a kinky thing. You helping her because her hands are too small. Or whatever you come up with. After a few times, she'll either catch on to what you're doing and change her methods freely or you're gonna have to bring it up. "Hey babe, I kinda liked how you did it last time".
Or go for the direct approach as Charles suggests. But even at that, you're gonna have to show her what you like. How fast, how hard, how much lube, etc. Personally, I wouldn't have a problem switching up my game if a girl said she didn't like something I specifically did. People aren't mind readers! Oooo that's another angle you could play. Tell her you'd prefer if she did it like <blank> and then ask if there's anything you could improve upon.
