I guess socializing is really one thing a parent can't teach. It doesn't sound like she doesn't know how to make friends since she has friends from other classes. When I was younger, my best friends were also from my neighbouring class and every recess time, I will hang out with them and not the others in my class.
Speak to her and see if this is bothering her. If it is not an issue to her and she is alright with not have a lot of friends and just a few better ones, then I think you need not be too worried. Just always assure her that she is likable and make her feel confident about herself. Also, keep a lookout during puberty period where one become more concern about one's looks and how others perceive one.
Take care mummy. Let your girl blossom on her own.
Read more