Kevin here's a neat trick to help her makes sure she stays hydrated. Leave 5 medium glasses on the counter next to the fridge. Tell her she needs to use 1 glass everytime she has a drink of water and they all need to be used by 6pm.
I tell you we did this for my aunt who was 90 at the time and was always telling us that she was drinking fluids but we knew she wasn't so to show her what she was really drinking we did this and she never had to go to the hospital for dehydration again! It would be so funny when she would come into the kitchen and see the glasses and make faces that she still had more to drink. She passed away 1 1/2 years ago at 101.