Different groups of 'they' tend to support different sides.
Her family will probably support her as yours will support you.
Her best friends are going to take her side, but you'd expect yours to take your side, right?
Yet, moving on…maybe things can go to the next level where no one has to take sides.
Could it be that you and she rise above any temporary anger and hurt, handle things in a mature manner, and not ask anyone to take sides at all?