Self flushing toilet. Anyone have one at home?

try one of the new touch toilets.

Can you convince mom to put the paper in a wastebasket next to the toilet? Also, she might not be feeling like she's gotten "clean". Baby wipes might be better; but they do need to be tossed rather than flushed.

I hate to sound like I'm so in favor of medication, but Cymbalta really helped my cousin with obsessions. (She has Vascular Dementia mixed with AD.) She had a drastic improvement. I might suggest treating the obsession and the anxiety that it can bring. She might stop obsessing with all the toilet paper. Besides, with my experience, even if she uses a couple of rolls of toilet paper, she is likely to continue an no amount will be enough. And if that obsession fades, another may surface.

I'm not sure what level of dementia your MIL has, but it's likely that someone with dementia may disengage a device on the toilet that you might install, put soap or other items in the toilet or even eat the toilet paper. I have known of this before. It's like leaving a toddler unattended in the bathroom, IMO. They may resist or dislike the supervision, but it will likely become necessary.

I would agree it is an obsession. She will put depends in there too. And it happens more when she's upset. My FIL also lives with us and he is like a hawk not letting her have any privacy. This upsets her too.

Her bum is fine (we check) it upsets her so much not to use that much tp so we're trying to manage how we get it down. She will spend a loong time on the pot.

I don't know that I would work on the toilet, but more than likely focus on her being supervised. If she's doing this is could be an obsession, but nonetheless, she could be rubbing her skin raw too. I think I would insist on supervising her toileting at this point. She could also be putting other things in the toilet.