Oh, for heaven's sake, let her take the dang vibrator. It's not the end of the world if someone is trying to explore their body. My son has been telling me he's going to have some "private time" in his room for a year now and asking me not to come in, and he's only 9. Buy yourself a nice new one and give the old one up as a general family possession that is now probably somewhere in your daughter's room. :)
I was thinking of a category like this -- growing up with a lot of people in my family, my mother would buy a package of hairbrushes and put them in the bathroom. Every now and then, someone would take a liking to one of the brushes, and then that particular hairbrush would be kept in their own dresser drawer. In other words, an item that originally just belonged in the house somewhere got claimed by someone to be their own. Mom would just buy another package of hairbrushes. I wasn't thinking of some kinky image where people shared their vibrator around. (I was also thinking of a more generic-looking massager, not something that looks specifically phallic. Guess that was probably innocent of me, you did say vibrator and not massager.)
Anyway, I don't see this as anything to discuss with her, toss it if you want to or just hide it better, but don't embarrass both of you by bringing it up. The fact that she returned it suggests she isn't hoping she owns her own.
She has since returned it to its spot. Yes I will be throwing it away. I definitely don't feel comfortable with the "general family possession" remark. As I know these things are natural, the basis of my question was how to speak to her about it without embarrassment on both our sides.