Well, you have some wonderful advice posted.
In my opinion, If your wife has a bashful personality, you don't want to embarrass her. She won't open up if that happens.
However, if she's open and freaky, than bring it up when ever YOU feel comfortable. The more comfortable you fee the better you deliver your concern about her vibrator.
The goal is to make her feel comfortable, so she can discuss her secret. If you're down, use the vibrator during sex, if she wants to, or let her keep that special toy for her personal use only.
Another thing you have to consider, are you really pleasing her sexually?
As quiet as kept, I've been with my husband for 3 years and he doesn't please me sexually, but he doesn't know that. I can't hurt his feeling and/or pride in that manner.
I masturbate to release my own orgasm, and he doesn't know. I'm scared to put a strain on our perfect relationship, so i put my feeling to the side to please him 100%.
Is it fair for me? I think so, When I asked for those new expensive drapes, he paid for them when he didn't want to. Quietly, I hate his style of love making, and he hates buying me unnecessary decor around the house...tee hee
Its a give and take in my opinion. Look within your marriage and put things in perspective. You'll find the answer. I wish you the best nevertheless!