Recently I finally made myself clear out most of what was left of Mum's clothes. Before a pair of trousers went off to the charity shop, I had to undo the last, very tricky tangle of knots she tied in the waistband tie. It was unexpectedly emotional, knowing I was undoing a knot she tied, maybe five or years ago.
Back then she went through a phase of tying knots into absolutely everything that was knotable. Not just one knot... as many knots as she could manage. It kept her busy hor hours. As long as she was happy, I was happy... though it could be a bit of a nuisance. Ok, a lot of a nuisance.
I decided the knotting was Mum trying to stop things falling apart... to impose order on the chaos her life had descended into. I was probably completely wrong. She might just have been desperately bored and seeking an outlet with limited ways to communicate tha! But you have to try and find something positive in most dementia behaviours... otherwise you'd go insane.
All the best to you and your Mum. It's not easy.