I understand what you are saying.
I am the type of person that is able to speak up when others are starting this nonsense. But I have learned that not everyone has the energy or the tools to stand up for others or for what they truly feel.
It takes maturity, self confidence and energy.
Your friend is just not there yet. Why? A million different reasons.
You will need to make an effort to just stay out of all of the drama going on over there and allow this friend to be your friend, but not need to be your spokesperson.
Your time with her needs to be about everything except that group.
I have learned I do not need drama. I really try not to get pulled into it and not to make others be apart of it. If your friend is not standing up for you, maybe her silence, is her way of just staying out of it.
As we mature, we begin to realize that we do not have time to waste on these childish behaviors. You are in a different place than these other people.. You have outgrown them.. This will continue to happen for the rest of your life. Just put them behind you and move on.