I had this problem with MiL, but I could get her to eat ice lollies. Made them myself from no added sugar squash and they were at least 90℅ water. She like the ribena ones best.
My elderly friend is now in a nursing home and is suffering from dysphasia as well as dementia. She is hardly drinking despite efforts of encouragement. Does anyone have any ideas on how to get her to drink? She is 94 years old.