My mum wouldnt allow POA either, but not because she denied memory problems, but because she thought I was stealing from her (I wasnt), so I had to wait until she lost capacity and I could then apply to the Court of Protection for deputyship (I believe its called guardianship in Scotland). After this I talked about POA to OH, who was developing symptoms and told him that I never wanted him to have to do this for me (I never mentioned that I doubted that he would be able to do it) and I was going to do POA, so did he want to do his too? He was at the stage where if I had something, he wanted one too, so he readily agreed.
We did mirror POAs which included our two children. I had to do it this way as if his POA was different, he would not have gone along with it. It does work however because I know that they will leave their dads POA to me, but if anything happens to me they can step in as OHs attorneys. I also know that if anything happens to me OH will not be capable of being my attorney, but the children can do it. If you feel that in order to get your mum to sign her POA you have to make her your POA, then do it, but simply only send her POA off to be registered and destroy yours afterwards.