I found a wonderful book at last years library book sale...I suggest you get it.

The Odd Girl Out:
http://www.rachelsimmons.com/index.htm

She interviewed many adult women and found similar stories about being
socially bullied in school. Then she decided to interview the girls themselves IN schools across the country. The resulting book is disturbing, but also cathartic. Girls can be very very cruel, to others and they seem to pick
victims. Understanding this dynamic may help overcome the cruelty.

As far as helping a sensitive young person, I'd try some inositol first to see if that helps. My husband and son had good results with this, and it was easy to do.

We buy the powder online at iherb.com
Start with 500mg/day and work up. Psychiatrists use very high dose up to 15grams daily for OCD. We found that 2 grams/daily was very effective.
I'd have supervision for anything over 5 grams.

Locally purchased inositol is expensive.
This is what we use:
http://www.iherb.com/ProductDetails.aspx?c=1&pid=126

It mixes into juice with no taste...it is pleasant actually.
Since SSRIs are the first line for social anxiety --you can also try to
increase serotonin naturally yourself. B6 (preferably in P5P form) and
L-trytophan may work as well. But I'd try the inositol first. We've been using it almost 2 yrs now, and my husband is MUCH more comfortable with people as a result. Wish I knew about it in the past.

Basically I think the best method for dealing with anxiety is to keep active and confront it. Doing "something" rather than obsessing, helps dilute the feelings and helps build esteem. Therapy can help with this, but the patient herself has to do the work.

Good luck.