Why does pecola goes mad?

She basically lives a life that is nothing short of Hell. She is raped by her father, Cholly, in the spring, and becomes pregnant. Her baby comes too early and dies. Terrified of her parents, she is not free (due to gender and age) to run away from home as Sammy does. Either during the pregnancy or after the miscarriage, Pecola goes mad, manufacturing an imaginary friend who becomes her only conversation partner.