R.A.
Does she participate in an outside activity such as sports or dance? That's a good opportunity for her to establish friendships. I have one child as well, and he is very social so he doesn't have difficulties finding children to play with, however he has had incidents when his friends are off playing with other kids, or have not invited him to play or sleepovers. I've told my son that it doesn't matter, and sometimes you have to put yourself out there and ask to play or sit with friends. I've also initiated having kids over to play as this also helps establish social skills and friendships. Other times you just have to play it out, and find opportunities as they arise.