An 11 year old should be allowed to play at others' houses and invite friends for overnight. If you are uncomfortable with her friend's parents, you should invite them in for tea or coffee or lemonade or a beer, whatever you are comfortable with. She is missing out on lots of important social situations, and also is learning to fear normal people : <
I think you're being way overprotective, to the point of stiflilng her socialization.
I can sort of understand the no sleepovers, I'm not like that but I can perceive that.
Not allowing her to visit friends houses except for birthday parties? I don't think she'll be able to develop normal, deep social friendships that girls thrive on if she's not allowed friends outside of school.
I do agree with Agiesmom that it's great to check out the friends, and ask questions like will the parents be there the whole time, are there guns in the house.
I've been accused of being overprotective, but I think it's good to be cautious. I won't allow my son to go into the neighbor boys' homes to play because I've never been in their homes myself and I don't know their parents--even if you meet someone a few times, you don't really know them.
Another reason I'm cautious is the fact that people here have guns. Lots of guns. So unless I come right out and ask (and I always do), I have no idea if they have guns and where and how they keep them and that's a big issue for me. I have insulted people by asking that question when arriving at their home for a party or dinner. I usually get a reply like, "We have them, but they are locked away and are not loaded." But more times than I care to remember, I have not received a reply with which I was comfortable. When my son was 6 (he's now 11), he had a piano teacher who had two sons (one my son's age) and the boys would play for a half hour after ds' lesson. Well, when I asked if they had guns, she said, "Yeah...we do keep a loaded rifle leaning in the corner of our bedroom, but the boys know not to ever touch it. When I looked horrified at this reply, she yelled, "Boys...stay out of our bedroom!" Yeah...that's not going to work for me. I'm of the "better safe than sorry" mindset. I just think that no matter how much you drill something into a kid's head, you just can't completely trust that curiosity or the desire to show off won't take over, never mind what a visiting child might do.
So, no...I don't think you are over protective. (And you're probably thinking, "At least I'm not THAT bad! ;))