S.H.
My daughter is like this and she is 12! She is the oldest and has three younger brothers. It drives her insane if she has a friend over and the friend wants to do anything that includes her brothers especially the 11 yr old. She gets super upset if one of her friends "likes" her brother but is tickled pink when its the other way around. I also have this issue with my 10year old son who rarely even wants to have friends over because he says they always want to hang out with the older two. I dont have any answers for you sorry, but I am in the same boat.