In these groups, there's often a queen bee and someone who challenges her, and then a bunch of followers. That's how it was when I was a kid, and also in my kids' groups.
I was a follower (with my school group friends). It was easier. I then had enough in junior high, met my real friends, and moved on. I'm still friends with those gals to this day.
I hope that happens for your daughter. I suspect it will.
The thing is, the followers are forced to pick sides. They are seeing what happens when that happens. They don't want to be bullied either .. so they picked the alpha girl's side.
I'd just explain that to your daughter. It sucks, but that's how the group dynamics work (especially school groups).
It's too bad your daughter didn't just drift in a way - rather than a standoff? Was that it? How did it go down?
A lot of girls (mine included) don't like drama or showdowns. So they would side with the girl who didn't cause the upset in the group. It may be that too - if your daughter finally had enough and changed how the dynamic is.
I suspect they like your daughter still - just don't want to get involved. Remember - maturity levels are super low at this age. High school is much better.
They probably feel are in a pick and choose situation here. They don't see it as they can be friends with both.
I would just encourage your daughter to be involved in other things, seek out some new friendships (or maybe hang out with one of the girls she's closer to), or a friend she's pals with outside of the group. Getting one away on their own can really help - maybe suggest a movie date, etc.
In a week hopefully it won't seem to so bad. I just listen .. because they just want to get it all out and know that they can talk. Good luck :)