I am so sorry to hear of your grandfathers passing. I know everyone is greiving. Maybe the stress of watching your grandfather grow steadly ill, has been too much of a strain on your mother. They say there are stages to grief. My mother, the sweetest woman in the world, became "short" during my grandmothers illness of altizmers. The stress was just overwhelming.
I hope things improve with your mother.
Again- I am so sorry for your loss. I will put the family in prayers.