In my personal experience the louder they cry nothing is wrong the more they know it is.
I really don't think your friend is in denial like you think, clearly not, she has talked with you about this before it escalated. What she is…….is at the end of her rope, backed in a corner with no alternatives left but to leave him. As long as she doesn't acknowledge that to another human being she doesn't have to DO anything about it. What you are seeing is just a small pebble of what its really like there at home.
I agree with the others there isn't an awful lot you can do here. I will say this though - if you choose to move forward with talking to her make it a 1 on 1. Could be risking the friendship ……but, but, but……..gee what are friends for except sometimes to tell those things we just don't want to hear.
As for the sexual assault - it is most unfortunate charges weren't filed.