Where to begin... such a bad movie. Lots of bad things, especially the fact that the writer plays three characters, including and old man and an old woman. I've never understood the humor in not having old people play old people, but whatever. I also have issues about to how we're supposed to see the "mad black woman"'s "strength" in physically abusing, including nearly drowning, her husband that is at the time quadriplegic. That takes a whole lot of courage, no?
Anyway, the most disturbing part of all - running throughout the film - is the gross misrepresentation of family law. The whole premise is that her lawyer (and huge jerk of a) husband made her sign a prenuptial agreement, thus is able to kick her out of the house with no place to go, stop paying for her mother's care, and give her no money. Not even her own lawyer (and cousin) tells her that this is not an open and shut case.
Prenuptial agreements of the kind she has aren't worth the paper they're written on. There's every reason to believe that she didn't have any legal representation when entering the agreement, or if she did it was clearly inadequate. Especially with her husband being an attorney, any court would be highly suspect of her waiving all rights to the property. And many states specifically prohibit the designation of who gets to live in the marital home upon separation.
Her husband would be required to help her maintain the quality of life she had become accustomed to over 18 years of marriage, especially considering that she has no skills with which to earn a living beyond entry-level unskilled labor positions. The fact that they were married for 18 years is also of great importance. Good prenuptials frequently escalate the amount of property retained by the poorer spouse based on the length of the marriage. Among other reasons, this is done to increase the probability of the agreement being upheld.
So there are plenty of reasons to dislike Diary of a Mad Black Woman, and especially its depiction of law. Other misrepresentations in movies present a more complex question, such as Dodgeball, a fine flick... until you get to the terrible ending.