Over Protective??

So my 8 year old ask me today if she could sleep over at her friends house and I told her no.She obviously was upset because she thinks she is old enough to do so. I wanted to give her my reasons why I wasn't comfortable with it but I don't think she would be old enough to understand. I think I am just afraid of something happening to her and me not being there to protect her. I was molested at a very young age and it would kill me if I found out that anything like that happened to one of my kids. Is it wrong of me to worry? I don't think it is, I mean I have a good reason to feel how I feel. I am put in the positon were I don't even know at what age I would be comfortable with letting them spend the night anywhere or walk to their friends house across the street. Maybe I shouldn't let what happened to me get in the way of raising my children. I am so confused over this. Some might call me over protective but I say I am just a concerned mother. That my opinion and for now I don't think I will be letting any of my children do sleepovers anytime soon. What should I do?