Hello there. This's just my understanding, but I'd have thought that as wills and PoAs are legal documents there would have to be the mental capacity to know what you're signing up to. For instance, even if someone is no longer capable of reading the PoA documentation for themselves, they need to understand that they're offering the power over their finances to someone else. They don't necessarily need to remember this in the long term, but need to understand at the time of the documentation being signed and witnessed.
Your post reads as if you're thinking your mum may have moved beyond this. In my experience it then requires a professional (eg medical consultant) to state that the person is not able to understand the contract they are signing due to whatever reason. You're then looking at going to the Court of Protection to get deputyship over property and affairs.
