Why does mom deny bowel movements and bathroom visits?

I am laughing because of these incontinent problems some are hilarious unless of course it's you dealing with it. But praise God I have to laugh about some of the conversations. I will say "do you need to go to the bathroom"? and she will say "no I am not going this week, today or this year". LOL And then when she has a bowel movement and I show her and say "that was a good bowel movement (because she was always one to watch her bowels and did suffer sometimes with constipation) but now that she is in a later stage of dementia, I do not understand her denying the bowel movements. She will say, I did not do that very sternly she says it. And then to get her to go to the bathroom, I have to make up all kinds of stories, bribes for ice cream afterwards. And then she will say no and go on herself if I do not catch her having body language that lets me know it's time. This is very restraining not being able to leave her side watching for those "Times" after a meal and of course with no exercise, her body does not respond as ours does because we get more exercise and we often go the same time each day. Any ideas? I guess it is better than having a mom OC about going to many times to the bathroom like I am reading on this post. She has OC about other things like wanting scissors to cut up books or folding multiple tissues. We end of just tearing pages from a magazine and that seems to soothe her and I find folded tissues everywhere. She is 87 and I am happy I still have my mom but it sure is trying at times