What is the function of Lucretia?

She seemed like a hard character to place. Mostly she seemed kind of like a bad fiance, all she ever did was nag Vince about his diet, behavior, opinions. IN fact I think she was kind of Mrs. Jealousy, we see her early on in the film berating Vince for staring at the lead actress in a movie. But it was always portrayed as though Vince was the dysfunctional one. I attribute it partially to the nineties trend of having angry women in movies to offset the bimbos of past decades. And then also at the end Vince's vows were so long and thoughtful, and hers were like an afterthought. I mean, were we supposed to like her? or was she a mirror for Lester's bad qualities?