You can provide some clarity

 

and let your daughter find her own solution, realizing that not all problems have solutions, mitigation, maybe.

Sounds like she is not the leader of the clique, only a follower.

Some questions to ask her:

- How many girls are in the group?

- Who seems to be the most influential among them?

- Who follows the leader most closely?  Do they act like the flying monkeys in the "Wizard of Oz"?

- Do you like the leader as a person? What are her good points?  If she decides she doesn't like you anymore, what would she likely do?

- You need friendship from the leader, or some other girl in the group?

- What does she likely say if you start playing with the lonely girl?

- Do you feel you are obligated to play with the lonely girl? Why or why not?

- If you don't feel like doing something, under what condition would you do it? Where do you draw the line?

- Who's need comes first?  If yours and other's come into conflict, how are you going to decide?  If you don't make a decision in time, have you decided to let the situation decide for you?  What's the criteria?

...