AITA for excluding my DIL from holidays

ETA: Thank you everyone for the responses. I'm actually said daughter in law who is unfortunately going through this very real situation. I will be printing screen shots from this to give to my MIL as a Christmas present (I'll be sending them with my soon to be ex husband) and then promptly handing her son divorce papers when he gets home from their holiday meal. This whole situation was the final nail in the coffin of our already pretty dead relationship. Every rationale I've given in the comments were things she said to me when I asked her why she was more mad at me for coming to her than she was at her son. So again, thank you all.

Am I the asshole for excluding my daughter in law from the holidays?

Last year my DIL, emailed me proof of my son being involved in an extra marital affair with a coworker of his and tried to ask for advice. The messages were extremely graphic, and not something I needed to see about my son. As far as anyone knows the affair never went beyond graphic messages back and forth, but they were separated for a time. They got back together over the summer despite my disapproval of the situation as she could have ruined his career with those messages. He has worked very hard to get to where he's at in the company and that is something I take a lot of pride in. When I explained my disapproval of their reunification he explained that there was nothing to blame his wife for and that he was in a bad spot and should have gotten help instead of speaking inappropriately to a coworker. I told him she would no longer be allowed at any family gatherings as I cannot stand to be in the same room with her after what she sent me. She embarrassed with those and she almost ruined my son. Now he's extremely upset I won't allow her around for the holidays and is considering refusing to come to dinner since he does not want her spending the holidays alone as she has no other family besides him. Both of her parents are gone and she is an only child, which I can understand would make the holidays lonely, but I can't get over the embarrassment. Am I in the wrong for not wanting her around?