Mam never drank enough either, but I tried her with those small cartons of juice that come with a straw, she enjoyed those. I find it helps with dad now too. Sometimes they find it easier to drink more if it’s through a straw.
other things can be soups, ice lollies, tinned tomatoes with the juice, even gravy. In the summer particularly I get the packs of prepared melon & some grapes or pineapple. I put some in a small bowl & he enjoys them.
When I give him juice or a glass of water, I remind him that the doctor said he has to drink more,that often helps. Somehow the word ‘doctor’ has magical powers (at times).
I hope some of that might be helpful. Best of luck, it’s not easy