What to if you are forced to look after a child with bad behavior and the parents make excuses for the child?

I have a good friend from church She is the leader of a GS Brownie troop. She has this one child who's behavior is out of control, She bullies the other girls and lies and creates all kinds of problems and the mother just makes excuses for her. The mother is also a bully and insist of bending the rules and is constantly filling unfounded complaints on my friend when things don't go her way. We are part of a Catholic church so the Mom is always quoting scripture. My friend is beside herself and even considering stepping down from her position just be free of this Mom. This little girl is not the only child who acts out so she feels guilty because if it weren't for the Mom she would just deal with it. But she is finding harder and harder to deal with child when the Mom is such a problem. The other Moms see it too but they do not want the vindictiveness of this Mom to turn on them. I wish I could help her but I don't know what to do. I see how tormented she is with this.