Might Prudie's mother have had senile dementia?
I mean, Prudie was thinking of her mother (Mama Sky) as irresponsible and uncaring, but it seemed to me that it was actually backwards, that Prudie wasn't aware of the struggle her mother was facing, you know, as erratic behaviours are very common once a person has some condition that affects their psyche, and hence, their behaviours.
In fact, her mother ending up dead that way seemed to me a direct consequence of she being left uncared (as Prudie told her to get out of her apartment).
And yes, I saw the scene in the car in which Prudie tells the guy that her mother reminded her that if she didn't like X stuff last year so why she would get it again? but well... wasn't that an strategy of mothers of that time? I don't think it was necessarily ill-intended.