I was offered some giants not too long ago and when I asked this same question I was told that the giants will eventually try to eat the regular sized ones.
I used to have several giant females in with my standard sized females and they were always fine. In fact, I found my giant females were actually often more docile than their smaller counterparts.
I never had a giant female try and eat or attack any of the other females.
The success of a sorority really comes down to the invididual personality of the females in question.