It does not happen every night. My mom does wear disposable underwear daily and nightly but I think going pee that often is too much even if it only happens once or twice a week, right? I do limit her liquid intake at night. She is diabetic but it's controlled. And she does take one incontinence pill (Vesicare - 5mgs) daily in the morning.
I expect/hope this is a stupid question, but she wouldn't happen also to have been prescribed a diuretic for any reason, has she? Stranger prescriptions have happened…
The other point with frequent getting up at night is that you have to wonder if she actually needs to pee, and it's waking her up, or if she wakes up and therefore notices that she might as well go for a pee.
Keep an eye on volume (easier if she uses a commode) and check for a u.t.i.; and other than that is it actually a problem for her or for you?
I put Poise pads inside her overnight brief to keep her dryer.