I wirk in a locked Dementia Ward.
I think you should look into getting her into one of them.
Yoyr Dad isn't coping. It will be only a matter time before your Mum ends up neglected, starts having falls, etc. Not wilfully neglected. But you can't expect an elderly person to be caring for an elderly demented person. It is near impissible to do so and still keep your own health.
Demntia sufferers need 24/7 in a locked up place, where they can roam and still be very safe, with carers on hand.
Most of our Dementia sufferers come in not in the best of conditions. Problems with their hygiene, due to being resistive to cares etc, usually nasty skin issues, sores, just general unhealthiness, because despite family thinking they are doing the right thing...... they fail, because they can't see how bad it has gotten.
Do yoyr family and Dad a huge favour and put your Mum into care. You will find after settling in, she'll do very well. Better than out in the big wide scary world.