How ''Precious'' saw the world...
So we're seeing the movie basically through Precious's eyes and possibly even her perspective. Is it possible to say that Precious had a victim complex and things are not exactly as they appear? there is certainly a chance that she's been coloring her reality more negative than it truly is.
The relationship with her mother for example, Mary is portrayed as a monster through Precious's perspective but if you analyze things from a distance you will notice none of Mary's rage has anything to ''do'' with Precious. She was mostly a housebound woman who sat in front of the television in a state of misery. Her outbursts could have been at anyone, she went after Precious just because she was there.
Also Precious spent two extra years in junior high never bothering to tell anyone she couldn't read. She is prone to disassociation (her ''fantasies'') and seemed to be generally apathetic to making her situation any better (until the end).