Ummmm. That is great taht you are able to be open with her in discussing sexuallity. In these days and times you really need to be. Kids will find answers somewhere. I would it rather it be a parent then another kid or a website.
As for buying your 12 yr old a vibe. I'm not so sure that is a good idea. Hopefully in life she will not need one. Unfortunately we ladies can develop a dependance on our battery operated friend. It is very hard to reverse that. In my opinion that is setting her up for failure.
Let her experiment in her own ways, and if a vibe is something she would like to purchase let that be up to her and her husband one day, or her and her bf one day, or her as a fully developed mature lady who knows what her sexual needs are. I wouldn't go pushing that kind of thing on a developing grils body and anatomy.
That's just my opinion.