There is no absolute right and wrong in terms of relationship ethics. Obviously, it's not OK to exploit or abuse someone but working out what specific behaviours are acceptable is down to the couple.
If you are uncomfortable with her using her vibrator, you can do three things:
1) Convince her not to use it anymore
2) Deal with your feelings and not expect her to change
3) Leave her
Being in a relationship does not automatically mean that you have exclusive rights to her sexual pleasure, vagina, emotions, etc. The limits of the relationship are something you should mutually decide.
In terms of what you should do - work out why you feel the way you do. What about her behaviour is threatening or upsetting. Do you feel entitled to 'cash in' on these feelings by asking for a change in her behaviour or is this something that is better handled by you trying to overcome your emotions? What are the risks involved with what she is doing?
Personally, I don't see sex toys as a threat. Being with someone doesn't grant me the 'keys' to their body and soul. I don't feel 'reduced' or 'diminished' by not being the only source of pleasure in my partners' lives, and don't worry that sex toys will prove to be more satisfying than intimacy. I had a partner who would only allow me to use sex toys if they were used on my by him. He kept my sex toys at his house and wouldn't let me have access to them without him being there. Frankly, it was a laughable situation. I wasn't allowed sexual pleasure without him and although there was no risk of STDs, pregnancy, intimacy or love from these objects, he still felt entitled to censure my experiences. It was suffocating and the relationship fell apart because he couldn't get over his whims and jealousies.
You keep asking why it's right that she uses toys - why is it wrong?