There are vibrators and there are vibrators. With personal battery operated devices it would be prudent to discuss the matter, first. With the large AC powered devices used for body massage, I do not see any reason why it cannot be a surprise. That said, those larger devices can also be used for more intimate pleasures as well. Begin with a general body massage and then transition if it is her wish.
Two machines have had a great and long reputation: The Hitachi "Wand", and the Wahl "Coil" (with interchangeable heads). Here is one very reputable business site:
Good Vibrations in S.F.
The "Wand" can be used to stimulate the clitoris and vulva by cupping the ball with the hand and extending one or two fingers to transfer the vibrations. (I do not recommend using the ball directly on the vulva.)
I hope this is of help. Got questions?