Your timeline isn’t clear. If she knew about his past when she married him, she invited herself to that party. And this sentence doesn’t make any sense at all. “And it was just a “she said- he said situation” as there were many neutral 3rd party witnesses to the abuse”. Not sure what you were trying to say there. But it doesn’t appear that you got it said.
Few people are objective when selecting a bed partner. If they opened their eyes and vetted their children's potential parent, most of this could be avoided.