Today's delimma

My daughter has been invited to a slumber party. She’s 7 years old. For some reason I feel this is just a little young for a sleepover. I’m sure I’m just projecting all my stuff on this. She already slept over at a child’s house before but that was because of a flood and we couldn’t get her home. She didn’t have a problem then. So I guess that excuse doesn’t hold weight. My biggest thing is this. The girl that invited her is part of a group of girls that my daughter doesn’t really do much with. They don’t play together at recess, they don’t have playdates…in general they just don’t seem to be “friends”. Now ya see, I say that but my daughter would tell you EVERYONE is her friend. I like these girls individually, but as a group I have seen them exclude certain children from their reindeer games.
I worry that H will feel left out once she’s there and that she will realize how different she is from these girls. H already wears her heart on her sleeve and has feelings that she is different and people don’t like her. (Sounds kinda depressive eh?) Have no fear we’ve discussed this with her doc and for my child this is normal.
So, should I let her go? I really need some feedback on this. Am I trying to shelter her from the real world too much? Is this a good chance for her to find out if these girls could really be “friends”?
Should I just pull my head out and quit worrying?
There ya have it…give it to me straight folks. I need to hear it.