Gently, I would encourage you to not view it as "The friend decided that DD was expendable and cut her loose." They are 5.
This was the first thing that popped into my head as well.
Both my kids had extreme difficulty at that age - DD with the intense behaviours that you describe and DS with a complete lack of understanding of social cues and difficulties with pragmatic language (he's not on the spectrum - after extensive evaluations we've ruled this out - but I think he's somewhere near it).
In fact, it got to the point, at the end of grade 1 when DS was 6, that I considered homeschooling him for a year so that the other kids could "forget" the damage his quirky behaviours had done. His teacher talked me out of it, saying they were making progress with him and had a plan in place next year.
They are 9 and 10 now, and WHAT a difference. It's to the point where I'm mulling over pulling DS9 from the social skills group he's in because I don't want him missing more class time (I don't think I will - but he's so socially skilled now that I wonder how much more he can learn in the group - maybe he's like a mentor for the newer kids).
Anyway, five was a difficult age for us, but it's gotten so much better
