7th grade is AWFUL... the girls morph into little harpies and social jockeying is how they feel powerful.. It will pass...
In the meantime, I agree with the suggestion to have your daughter invite kids to do things with her, and organize get-togethers at your place.
Jealousy might be a motivator to the other girls excluding her. If she really is so popular with the adults in power.. teachers, coaches other moms, etc... the exclusion might be motivated by a power play...
While it tears your heart out,, there is really nothing you can do... I feel for you, as I have a 17 and 13 y/o and I have been there, done that. (Actually I was like your daughter) It DOES get better... in the meantime, be supportive and loving and available to listen and hug...
Unfortunately there's not much more you can do other than the wonderful suggestions that were offered here.
Good luck, your daughter sounds like a lovely girl...