why do you think nana kills herself?

Nana's emphasis on Mariam learning to endure suffering not only suggests how bleak Mariam's future will be, but also the type of lessons that Mariam must have learned as a child in Nana's home. In the end Nana could not endure her own suffering. Her life was the culmination of abuse, disappointment, and abandonment. Mariam's adoration of Jalil, just made matters worse for her.