He wasn't prosecuted in a criminal trial because her own friend who was there didn't back up her story. And while she did have a tampon wedged in her, it could have gotten stuck there through getting gangbanged consensually by two dudes. The bleeding could be explained by her being on her period, they weren't able to establish she had been violated for that reason. The primary evidence is the bruising and her own testimony. The standards for a civil trial are significantly less. Criminal trial is beyond a reasonable doubt, civil trial is it most likely happened. If the case had gone to a criminal trial imo it would have failed.
Her testimony of what Conor said to her has raised doubts in my mind. It just sounds fake, like a Khabib stan's bad fan fiction. Of course that means nothing to the people judging this case and there's no way to explain that to a jury. What also raises doubt for me is that she was able to recall exactly how Conor assaulted her and what he said to her but didn't even remember the other guy having sex with her as well. Is that dude on trial too?