Niles Crane met Mel by chance, learning she was the plastic surgeon of his ex wife Maris. Niles developed a crush and tried to see Mel as often as he could and they soon became an item. Upon meeting Mel, Niles' friends and family had nothing nice to say about her, finding her pushy, snobbish, rude, neurotic, manipulative, critical and incredibly selfish (all of which were true and traits Niles ignored). Maris began using her wealth and influence to discredit Mel as revenge for her dating Niles though it blew over rather quickly.
Niles and Mel eloped together towards the end of season 7, breaking Daphne's heart as she was in love with Niles. Through Frasier's interference, Niles discovered this and confessed his own eight year long love to Daphne only hours before her wedding. The two broke it off with their respective partners but Mel refused to be dumped after being married only three days, concerned for her social standing. Niles agreed to her proposal that they pretend to be happily married for a few weeks in exchange for a clean divorce, also demanding that Niles and Daphne not go out in public until then. When it seemed to be coming to an end, Mel decided that it would make more sense if Nile behaved highly boorish at high standing social events so that people would understand that Mel would have adequate reason to divorce him.
It became obvious that Mel was only doing this to be cruel, forcing Niles to humiliate himself and tarnish his reputation with the upper class over the next few weeks for sheer, petty revenge. She prolonged his torment for as long as she could and constantly forced Niles to break off plans with Daphne, relishing in how miserable it was making them both. At a party Mel informed everyone she and Niles would be taking a trip together, causing Niles to refuse to go along with the charade any longer. Mel fought back, cruelly insulting him and telling him he was not even close to being finished with her even though she had promised he would be weeks ago. Niles finally snapped, announcing his feelings for Daphne and dumping Mel, humiliating her in front of all her friends. Mel feebly attempted to keep playing the victim as her friends escorted her out and promised she would never have anything to do with Niles again, thus defeating her for good.