Hello blondeowl and a warm welcome to the forum, although I'm very sorry to hear of your concerns over your mum.
It will be difficult if your mum refuses help, but I've remembered one thing that has been suggested before in these circumstances, and that is for you to visit your mum's doctor yourself, and discuss all your concerns with them. Even write down the things that are bothering you, or a sort of journal of incidences.
Ask the GP if they would be willing to call in your mum for a general 'MOT', with the idea that they can see for themselves just how she is, and with the background info that you've given them they will be able to ask the right questions to give them an idea of what's happening.
It could be explained to your mum that all patients over a certain age are being called in, or all those who smoke, or all those who haven't seen their doctor for x number of years, or whatever is applicable to your mum.
Do you think that this approach might work? If so, it would at least be a start.
I'm sure others will be along shortly with more ideas for you to consider.