Hi welcome to Health care magic forum.
Thanks for calling H.C.M.F.
Your description says that your grand mother is at her last days unable to take any thing in side through the mouth.
With out knowing any details of the case it is not wise to comment upon the condition. It may be that she had some problem in the throat.
As your doctors advised you can keep her on morphine
and let her have infusions with a gap of 3 to 4 days to prevent hyper hydrosis
Wishing her a comfertable time.