Mrs. Greene is the matriarch of the family, but she's also the person who seems delicate and fragile to her children. Ever since her own mother died and she fell into a spell of depression, the family has kind of tiptoed around her, afraid to upset her and disturb the fragile balance. Because of this, Annabel is worried about telling her mother that she wants to quit modeling and that she was raped at a party—she just doesn't want her mother to grow weaker. Check out what Annabel says about her mother's depression:
There was something haunted and tired about her face, so obvious that even I, at nine, could see it. (2.65)
That's got to be a lot to make sense of for a nine year old, don't you think? But in the end when Annabel tells her mother everything, her mother surprises her—she totally rises to the occassion. Instead of shying away and becoming depressed, Mrs. Greene steps up to help her daughter and support her:
My mother had surprised me the most. She had not fallen apart, or crumpled, although I knew hearing what had happened to me was not easy for her. Instead, while Kristen cried, and Whitney helped my dad find Andrea Thomlinson's card in my room so he could call her for more details, my mother sat beside me, her arm around my shoulder, just smoothing her hand over my head, again and again. (19.4)
Annabel realizes that she's been wrong to just see her mother as weak this whole time. People are capable of more than you think.