A.K.
Your daughter sounds exactly like my son. In small groups or in places where he is comfortable he is the life of the party, but when you get him in bigger groups (especially with bigger more aggressive children) or in uncomfortable surroundings he clams up. I have found that the key to his happiness is to put him in situations where he has a comfort level or in small groups and then he does just fine. Some kids are more shy or cautious at this age than others. It is a part of their personality and it is okay. I have found that pushing my son into playing when he isn't comfortable is FAR worse than letting him find his own way. Let her be who she is and try to find social situations that provide her the sense of security that she needs.