Did you ask her the reason? that will help you. Be a good listener and share here
you care for your grandma that is really a appreciable one....ask about her past stories..or play any song or movie that she likes in her days....my grandma likes to speak with neighbour of
her age she usually do that to make her happy...see whether u can help with any of the above things...
I had asked the reason but she didn't told me
Try to do things that she likes and make sure that she has a sense of security and assurance that you are with her as a constant support system.
she is not even replying to our questions she is very much depressed but we don't know the reason because she is not able to tell the reason