That's really tough.
Crazz confided in two of his friends, both of whom were in our wedding. They both told him to "knock it off", and that was that. When I found out after DDay that they knew, I was both pissed at them for not doing something, and pissed at them for still being friends with Crazz.
After some time passed, I observed that one of his friends was really supportive of us working it out and went out of his way to try and be helpful and uplifting to our family. In a bit of a turnaround, I was grateful for him after that.
The other friend, who was Crazz's best man, avoided ME after Dday, but his mom "inexplicably" reached out to us to help with Vrazz if we needed - which we did. She was our babysitter while we went to MC, which was a huge help.
I was really upset and not considering this guy a friend of the marriage, but the night before his own wedding he cornered me and begged my forgiveness for his lack of involvement. It was a very emotional night, but the fence was somewhat mended.
I think that with lifelong friends there may a chance to revisit what happened and try and move on together. Do you think you can reach out to her to talk?