If your daughter knows how to use a
vibrator she probably has been using if for some time. If she has entered puberty to the extent that she enjoys masturbating, she is going to continue doing it one way or another until she outgrows it. You may be upset about that, but her hormones have kicked in and there is nothing you can do to stop them. If you have nto done so already, you should have a talk with her as soon as possible about the changes that are starting to occur in her body. She is probably ahead of her freinds and classmates in entering puberty, so she has a lot of questions and needs someone to answer them.
Your daughter using your boyfriend's
vibrator is another matter. You should make it clear to her that she should not take or use other people's property, particularly their personal things, without their permission. You do not have to mention the
vibrator specifically, but you do need to talk with her. If your boyfriend did give her permission to use his
vibrator, then you have a much more serious problem which you should discuss with your boyfriend rather than your daughter.