I'm a mother of boys, so I don't know specifically about girls, but my now 5 yo boy was definately starting to hide a bit around other children at 4 years old. I really noticed it in play. Alone, he would play elaborate make believe games with plots etc. With children his age, he would run around like crazy and just roar. He is my oldest, too.
So I guess I'm saying, it wouldn't surprise me at all if she was getting that message somehow.
I wonder what you do about it, though? I guess it depends on the child. In my case, I have been trying to expose my DS to other children who are perhaps more l;ike him, and older children too, so that he starts to feel like it is ok to be who he is.
