My elderly mother, age 70, who lives with me, has urinary incontinence and wears "incontinence underwear." She is good about changing them when needed but she is horrible about disposing of them. Most of the time, she just piles them in a corner in her room and maybe twice a week will gather them up into a trash bag to be disposed of. She lives with me, and her room reeks of urine. Absolutely disgusting urine permeated air hits you every time she opens her bedroom door. I bought her a "diaper pail" to put them in, but rather than put it is as soon as she takes it off, she places it in a corner in her room and after she has several of them will then put all of them into the pail. I remind her several times a week to use the pail every single time she changes her underwear, and I don't understand why she doesn't. She has never been very good at keeping things clean and put away, even when I was growing up. I have installed an air deodorizer that releases a medical grade deodorizing spray every 15 minutes and have given her a spray bottle of the same product to spray directly on her used underwear when she removes them, which she doesn't use. The automatic deodorizer spray has had some effect, lessened the urine smell some, but the main issue is getting her to dispose of the used undergarments correctly. I was even hoping to take her to her doctor and maybe a talk from him would help, but she refuses to go, and since she has not been deemed incompetent, I can't force her to go. Sometimes the odor is so strong it creeps into other rooms even though her door has been shut for hours. I am at my wit's end and don't know what else I can do.
Also, with dementia patients I find the problem is me and my expectation that they will line up with my requests/suggesstions of using a hamper, 'diaper pail', or spraying deodorizer in the room or their depends.
Their disease doesn't allow them to think in an orderly and linear fashion where action 'A' requires follow-up action 'B', otherwise consequence 'C' happens.
I had to adjust my expectation to their reality, as I can not expect them to align their reality with my expectation.
Try putting an extra diaper pail (or more) in her room, including her favorite 'corner' that she puts them in.
Is there much 'light' in her corner where she stashes them? If not, add a light (even a battery one that sticks on the wall with tape like they sell for closets and such). Having a light there may help deter her from keeping them there.
Other than that - you are really doing all that you can to mitigate the issue, and the odors.
On the 'bright side', at least she is wearing the underpants ---- and not going 'al fresco' all over the house.