Hard as it is you usually have to let these friendships run their course. I know with DD1 that if I just went along with the friendship (didn't actively encourage it but was never negative) then eventually she wised up and moved on.
At the moment your DD is prob terrified of high school and the fact that the only girl she knows going is a total back stabbing biarth means she needs to befriend her so she doesn't become her victim at high school (you know the term keep your friends close but your enemies even closer ?) I would write to the HS and ask that they be separated, your school may do that as well!

Hugs babe it does get easier eventually.