What happened to the girls mom?

It's never shown. From the time Osama begins being indoctrinated into the Taliba's ranks, until her discovery as a girl and being handed over to the Mullah, we never see her family. The focus of the film falls wholly on Osama and her treatment by the corrupt system. One can only asume that her mother and grandmother starve, as they have no man to support them. You, the viewer, are left to guess at their fate.

All I want is a warm bed and a kind word and unlimited power.