T.,
We could be talking about my son as well, he is 11 and it is hard for him to make friends. The good thing is that we (my husband and I) are always talking to him and letting him know how important he is in our lives and in God's sight. But he has always been like that. In kinder he only had one good friend. I've noticed that now that he is older he likes to look good, and it is proven that if we look good, we feel good. So, since our funds are limited and I have two other children, I try to get him some shirts and pants that I know he'll like. Old Navy is my friend when it comes to prices, but there is a thrift store not too far from us and there is a website called freecycle.org where I have been able to get some clothes in good shape for free. So if you can, reaffirm to her how beautiful, and important she is to you and your family. Don't give her any chances for her to be depress. Try to get her maybe one nice shirt, something she likes and what makes her happy. So when she looks at herself in the mirror she'll like what she sees.
Not everything is materialistic either, she needs to be told how special she is, that's why God made her :)
And pray for her, pray for God to send her way friends that will build her up, cherish her, love her and appreciate her. You can also try to invite some of the girls that are involved in sports over to your house for a 'girls night' or pizza, or even for just a movie. Try to open doors for her, that otherwise she won't open.
But most important, be there for her. And don't ever stop praying for her.
At least she is involved in sports, my son isn't, so I keep on praying :)