Well the mystery is at least partly solved - apparently the girl had not meant for my daughter to stay the night. She had planned a one-on-one sleepover with a friend she hadn't seen in a long time. The mom asked my daughter to stay, turning it into a 3-person sleepover - My daughter really wanted to stay, so I said sure why not, but the birthday girl felt jipped out of the one-on-one sleepover - And my daughter does tend to get a little rowdy when her routine is disrupted --- So it all sort of makes sense now.
I know all about teen daughters and their friends. I raised two girls
Bottom line. "Three" pre-teen or teenage girls CANNOT get along. Period
Two of them will "always" pair up and ostracise the the other one.
Later on the two who paired up as friends will have a falling out.
Then one of them will make friends with the ostracised girl
And now these two will be against the former friend.
It's like it is built into their girl DNA to act this way!!!