I would stop one inch away from cut direct. I wouldn't initiate any contact but would speak to them when they initiate, but I would keep it short and distant.
They should be apologizing profusely, not making excuses.
This exactly ^^^. I don't expect any apology, just more justification so, no initiation from me. I'm hoping DD will strengthen other friendships from now on.
P.S. this resulted in A LOT of last minute scrambling from our family (yes, under 18 restricted driver), a distressed teen meltdown, and a year of saving, planning, preparing on DD's part. I was forced to step in. If a legal adult doesn't want to hear how they threw us into upheaval...don't throw us into upheaval.
G's majority status, yet still close to DD's age, was precisely the reason I was comfortable letting her go overnight in the first place. When DD's in college, and mostly handling her own affairs my input won't be necessary. There are degrees of separation and HS is not there yet.