your best bet is to let her do it
or at least show you where.
my b/f will use one on me sometimes but of course he can't get it on my clit just right.
so i do it myself that way i can use the right amount of pressure...etc.
hope this helps

definately... put it between your teeth and suck, that should get her going.

yea the clit is where it feels the best
but like i said it would work better if she did it. you are just going to have to get her out of her shy phase. i used to be like that. i mean i dont see the difference if she's willing to use it by herself why she would mind if you were there. its not like she's playing w/ herself my using her hands. what difference is it if she holds the vibrator or you do?
anyhoo...
the only problem w/ going right for the clit is knowing how much pressure and such.
if its not on there right, you dont really feel much. if you hit it TOO directly then it kind of hurts.

Have her put her hand on top of yours, to guide it...so you're using it, but she's controlling it that should work. Maybe keep covered with a light sheet so she doesn't feel so exposed about the whole thing.