Sounds like for whatever reason, Betty doesn't know any better , but these other girls? I suspect they do & therefore the onus to behave better is on them. They are acting like utter twats under the false impression that they are somehow being righteous.
I've been in situations like this before both as a teen and surprisingly as an adult where this ' group think' gets out of hand and feeds off itself. I suspect none of the women would be behaving like this on their own, it's the group, pack mentality where people reinforce each other's bad behaviour that makes it ok in their heads.

If it were me, I would distance myself from all of them. I've found in the past that when in these situations if you find yourself the cheese that stands alone, even if the situation resolves itself (ie they stopped acting like rabid *****es) the relationship never quite recovers between the group as it only really functioned on the basis of dealing with the perceived threat or enemy. Once the threat goes away the group tends to start *****ing at each other and eventually dissolves.