My Mum Has Been In The Hospital Now For Past

My mum has been in the hospital now for past couple of months she is 90 years old and has lots of things wrong with her like Kidney failure heart failure and did have type 2 diabetis she now has gangerine in her toes of one foot now spreading up the shins and now spreading onto the other foot the dr has now says she is palletive. And only has a few weeks left as they cannot do any thing for her apart from keeping her comfortable my question is I have been up twice to see her and spend some time with her as I live 500 miles away and work full time it is now a week since the dr says she only had a couple of weeks left but my Siater says she is ok at the moment I have planned to go back up to were she lives but I don't know when to go back up to see her before she passes can you help please and advise me should I go now