Whoa whoa whoa... you two can't just start talking to each other and be honest within a chapter. This is supposed to take a couple of chapters where Grandpa, Dad and Daughter talk in allegories and evade questions
The mother's mother (so the grandmother) hated and abused her because she was the child of a man who just up and left the family. My interpretation of it is that the mother was kept sane and going through life by the burning hatred she had for the grandmother, however once the grandmother died, what keeps her going? Where does her hatred go? So it was thrust upon her daughter and those around her who cared about her.
Meanwhile she should have been sent to a mental hospital or taken medication, but she refused because she's an "artist" who was "inspired" by her depression.