Soccer is a great group sports activity for children your daughter's age. Not a lot of skill is required at that level, and all of the children enjoy running after the ball and trying to kick it.
There may be other groups which are not sports-related in which you could involve your daughter. Joining a Brownie troop or a church group may allow your daughter to become more comfortable in a group setting. She could gradually move into sports and game activities as her comfort level increases.