Hello, I'm just trying to get my head around what to expect

My grandma has terminal cancer and is on palative care.

She's at the now wanting to eat or drink much stage, she's breathless can go to the toilet with her frame but can't walk, where as 6 months ago she was fine.

The doctors have given her 2 to 3 months about 2 months ago.

I'm not sure what to expect or when to know when "the end" is expected, she sleep a lot has very slight confusion sometimes etc.

How can I help myum who is her full time carer? She's struggling as my nan snaps at her when she asks her to eat and drink just to take her tablets. 

Thank you for your help