I completely get it, OP, but I think you just need to suck it up and cheerfully tell her you want her to do as she wishes. If she's grown apart from the friend, you may luck out and she may decide on her own not to go. However, if you pressure her to stay, those precious extra days are liable to be spent with her hurt, angry, and resentful, sending her off to college with this hanging between you. Make the most of whatever time you have with her and hope that she wants to come home for breaks.