Make sure that your daughter has opportunities to make friends away from school as well. Joining a soccer team, a Girl Scout troop, or a church group can help her have friends who would be hers alone.
Fifth grade is a tough year for friendships, especially for girls. As they approach puberty, fifth grade girls go through lots of hormonal changes and experiment with independence; girls who have been close friends for years suddenly don't want to be around each other anymore. It sounds like your daughter may be seen as the friend who will always be there when others are unhappy with each other.