How to get someone to pull their pants down more on the toilet?

Thanks for the replies. Grandma is still pretty mobile. She can get out of bed and walk around the house by herself, with a walker. She mostly uses the toilet for #2 and her bedside commode only for #1. She has a rail in front and to the side and of course the two holds on the commode. I don't think it's because she feels like she's going to fall. She can take off her pants and underwear and put the pants on again by herself. Sadly she always neglects to put on a fresh pair of underwear. She can reach down all the way and put on her shoes. So it doesn't seem to be a physical limitation. She simply doesn't think she needs to pull them down any further.

There was no incident since yesterday. I had a thought that maybe she doesn't sit far enough back in the commode now. Those commode seats are smaller than regular toilet seats. So I move the commode 2" closer to the front rail hoping that would encourage her to sit further back. She holds on to the front rail to sit down. I'm also thinking about getting a commode with a larger seat. I already have one of those over the toilet. I think she only pulls her pants down until the front of the toilet seat. If she doesn't sit for enough back, then that's not far enough.

Grandma may fear that by pulling her pants down all the way, she’s going to lose her balance and fall. Do you have rails on the wall or a handicap toilet with rails? That would give her something to grab onto while she wriggles her pants down. Make sure her pants and diaper fit but are loose enough that she doesn’t need to yank too hard. That can upset her balance too. I agree with supervision. Help her sit down and then leave, but stay close by.

Your profile doesn't say what condition your mother has. Apparently, she is not physically or mentally able to master handling the full pull down up the pants. Either way, she can't help it, so, I would let it go and just always go with her to assist with it. If she has dementia, it's not likely that she is able to do what you are asking. And arguing won't help. She thinks she's right and her mind won't change. I would just supervise and assist her.

I haven't found a solution either, except to try and watch her and assist when she does go to the bathroom.
I have provided her with a low step placed in front of the toilet. This helps her overall and I haven't caught any accidents or wet slacks recently. I still try to watch her when she does go,