How To Ascertain That One Is In Coma?

A woman who is 50 yrs old, and has or had diabetes. Had an heart attack 2 days ago and the doctors declared her dead, but when her relatives went to visit they said that she was on the same room and she looked the same, and one of the move her arm up and let it go and her hand went down easily is this possible that her body is not that rough or hard? it is possible that she may be in comma?