Well, I can only speak from my own perspective here...for a woman that doesn't usually want/like sex, to have to put on a 'show' for her partner would seem very daunting and I imagine she will also feel a lot of pressure to 'perform' for you. And because of the pressure she may put on herself, she wont enjoy it and you could push her further away from you.

I really feel as though again you are thinking about yourself here. Getting the vibrator itself is a good idea. I think a better approach is to let her try it on her own and maybe work up to you both enjoying it. When she is ready to have you involved, I don't think its a good idea to watch her while she does it alone, I think it would be better if you started using it (on her) and then suggest she tries it herself while you are there?

I think this is a really good idea...but first she must be allowed to do it in private and maybe she can relax enough to enjoy it!

Good luck!