Who did you side with: Niles or Mel?
I personally think Mel was a shrew about the whole thing and was glad Niles ended up yelling at her in front of her friends.
Yes, she royally got screwed over. She married someone whom she thought was the one, only to have it fall apart within a few days because he had been in love with someone else all along. Niles never should have married her in that situation - he plainly stated to Daphne that he never would have married Mel had he known he had a chance with Daphne. That is horribly unfair to Mel that he would marry her without her ever knowing about his feelings for Daphne - she had a right to know, so that she could decide for herself whether to marry him. But at the same time, why did she marry him after only a few months? There was CLEARLY still a lot they didn't know about each other. She wasn't some naive teenager but a mature adult, a doctor for crying out loud. She should have known better than to marry someone who was just coming off of a divorce and whom she really didn't know that well.
And I'm surprised Niles tolerated Mel making such derogatory comments about Daphne, calling her a "whore" and contemptuously saying "your little English muffin." He had always gotten pissed whenever anyone so much as raised their voice to Daphne, and here Mel was saying these horrible things and he didn't defend her against that. Yes, Mel had a right to be upset, but Daphne hadn't really done anything wrong. Niles was stupid for marrying Mel when he loved Daphne, but really, in the situation they were in at the end of season 7, what should they have done? Stay with the people who were their second choice? Should Daphne have married Donny knowing she wanted Niles? Should Niles have stayed with Mel knowing she was no more than a consolation prize? Why would anyone want to be with someone when they know that person would rather be with someone else?
And Mel was just vindictive in the way she dragged things out. All for what, her reputation? She should have just let him go and not tried to keep up phony appearances. Let him be happy with the one he really loves rather than make everyone's lives miserable when no one was malicious towards you. It's ridiculous that she was trying to shoehorn Niles into spending his and Daphne's first New Year's Eve as a couple at a party with Mel instead of with Daphne. She was just being a shrew at this point. No one had meant to hurt her, but she was being deliberately malicious.