In The Jilting of Granny Weatherall by Katherine Anne Porter, why is Granny so hostile to Cornelia?

Granny might have a few different reasons for treating her daughter, Cornelia, with hostility. The main one seems to be that Cornelia is taking care of Granny when the old woman would rather be taking care of herself, which is frustrating and embarrassing for Granny.

But first, consider that her grouchy attitude may not be specifically directed at Cornelia. The old woman is simply in a bad mood because she's ill and dying, and in the process she's lost some of her independence and dignity, and so Granny treats everyone with the same cantankerous attitude. Look at how she thinks about the doctor and speaks to him in the first few paragraphs of the story; she calls him a brat and hints that he's just a child instead of an educated physician. 

However, when you consider how Granny utters hostile comments toward and about Cornelia, saying for example that she had to go to bed just to get rid of Cornelia, you might think the old woman's hostility toward her daughter is personal.

One reason for this attitude may be that Cornelia simply isn't Hapsy, the daughter that Granny loves best.

Another reason is that Cornelia has confined Granny to bed and has been whispering about her with the doctor, essentially treating her mother as if she were a child. "The thing that most annoyed her was that Cornelia thought she was deaf, dumb, and blind," the narrator tells us. You can see how that would irritate Granny, who is still somewhat aware of her surroundings and rather indignant at being treated like a helpless baby.

A few other minor things make Granny annoyed with her daughter. Cornelia's "good" and "dutiful" manners seem to irk Granny, who views them as exaggerated, ridiculous qualities. And Granny is tired of being contradicted by Cornelia. "[Children] disputed your every word," she thinks.

Still, when you consider how all those sad memories float through Granny's mind as she approaches death, you're tempted to conclude that it's just Granny's general disappointment with life that makes her treat Cornelia with hostility, rather than any issue that's specifically going on between the two women.