To get our elderly cat to drink more water, we bought a fountain. He loved it. All these years later, we still use the fountain for our cats' water needs.
Recently, our five-year-old had his second UTI infection within 6 months. Our vet put him on distilled water with cider vinegar, gradually increasing the amount of vinegar until he refused to drink the water, then backing off to just under that. Now both cats drink distilled water in the fountain, with 2 tsp cider vinegar per gallon of water.
Spot is also on
Dasuquin for Cats to strengthen his bladder walls to cut back on future infections. He gets two capsules opened and sprinkled on his dry food daily.
Alex shares the distilled water, so he's benefiting, too. At 17, he's pretty healthy for a cat who prefers to eat only gooshy food; he gets five ounces of canned food a day and still is a skinny guy. He doesn't like to squat, so his litter box is tall with a top opening. He can just stand and let go. But if your cat is having trouble walking, she might not be able to jump in and out of a top opening box.
Definitely have a vet do a full "old cat" workup on her, then go with what might work best for her. And all the best for you and your old girl.