Is it permissible for a grandmother to see her granddaughter in light clothing or nude when there is a need for that?

A Muslim must safeguard their 'awrah (private parts) from everyone except their spouse or what their right hand possesses, even if they are alone, because Allah is more deserving of shyness from. Therefore, you must be careful not to let your grandmother or anyone else see your 'awrah uncovered. This can be done by closing the door and relying on yourself to wake up, or by wearing appropriate clothing that covers the 'awrah.