Hi Monil, I'm sorry to hear about the situation with your daughter.

Here are some resources on Education.com you may find helpful...

Bullying at School and Online special edition:
http://www.education.com/topic/school-bullying-teasing/

Friendships info center:
http://www.education.com/topic/social-development-friendship/

The Parent's Guide to First Grade:
http://www.education.com/grade/first-grade/

Our daughter (who is also very social) had ups and downs with her friends in first grade too. We focused on listening to her feelings, being supportive of her (letting her know how special we thought she was; reminding her of the many friends she had outside of school), and discouraging her from demonizing the friends who weren't playing according to her rules, or who were excluding her from their games. We explained that we have a choice of who we play with, and that who we select may change from time from time, but that it doesn't mean we can't stay friends when someone doesn't choose to play with us (or tell them, "I'm not your friend if you don't play with me"). We told her she can choose to enjoy playing with someone new when other friends aren't available or don't want to play with her at that time. We acknowledged the disappointment (and sadness) that comes with not being able to play with the person she wants to, but emphasized the opportunity to play with a different game with someone else (or to do an activity by herself if no one else is available). These talks that we had multiple times that year didn't necessarily change the way other students behaved toward our daughter, but they did help our daughter in better handling the situation when friendships weren't going her way.

All the best to you in helping your daughter too.