Have you had the doctor or nurse check to make sure she's not getting a diuretic too close to bed time? Often they are prescribed twice a day, and if you don't know better, you'd give it at say 10 am and bedtime. But with furosemide, or other diuretics, you should take them as early as possible in the day - say 8 or earlier if you're up, then the second dose before supper so it has time to work before bedtime. Just a suggestion.
Also, in the hospital we have washable bed pads that are about 30" by 38". they are a cotton top, with a layer of padding, then a waterproof layer and then the bottom layer. The bottom layer is skid resistant so they stay in place. They can also be tucked up and around to reinforce an adult diaper.