Are you being protective? Absolutely. That is your job. As for being "overprotective," every 12-year-old I know uses that word to push a parent's buttons, to excite those feelings of guilt. You are her parents. You do know best.
In the meantime, prepare yourself and your daughter for the time she will begin dating. There are some excellent pamphlets and books on the subject that can help you out. Consult with your child's school counselor and/or at your local library. Discuss it with her. Look forward with her to that very important even in her life -- her first date.