I have talked with my daughter and explained that some times people change and hopefully one day the party girl will realize who her real friends are and apologize for her rude behavior. She and my DD have been through so much together and should get over this in time but I don't like the direction things are heading in.
I think your gut instincts about what direction your friend's family is heading in is absolutely correct. But it is hard to let go of a friendship that involves both parents and children.
I just want to ask, from your friend's behaviour (as well as that of her daughter), it almost seems to me that they are using this situation as an excuse to break with you & your family. Perhaps your different moral viewpoints make your friend more uncomfortable than you have realized. Because certainly a true friend would try to work through this situation instead of rudely blowing off and shooting off blame.
As difficult as it might be for everyone involved, it sounds like a definite cooling-off period would be in order. Especially if the girls don't even go to school together.
Good luck. And my compliments to your DD. She showed good judgement and moral strength. That's not easy in this day and age.