I was in a similar situation to you, and I lived an hour away from my mum, and was working almost full time, so could only spend one day a week with her. When my mum was at the stage your mum has reached, she was very resistant to having any support, other than me. I found a wonderful care charity who provided more of a befriending service, and were quite happy to never refer to their staff as carers when talking to my mum or to ask them to do traditional caring work. I was able to persuade my mum to meet the co-ordinator and he spent an hour with her to find out as much as he could about her to find a good match for a carer. It took some more persuasion before my mum woukd agree to have someone coming in, but she eventually accepted that she was a befriender who would keep her company for an hour each week. The agency always sent the same member of staff so they built up a good relationship. As time went on and my mum's dementia progressed, I gradually increased to four visits a week, and I changed the time so that the carer was there to heat up a ready meal for my mum.
My mum had recently stopped driving when her dementia began, and the lockdown had started, which made it easier to get her to accept the extra company when she couldn't get out to see her friends. I always told her that I wasn't going to push her into having carers to take over her housework , and she really did see the woman who came each week as a friend.
Once I realised that she wasn't cooking regularly, I paid for her to have meals on wheels so that I knew she was having a hot meal every day. It was also an added reassurance to know that the drivers were going indoors with her meal every day, and they always contacted me if they were at all worried.
My mum took a range of medication including warfarin and gabapentin, which had to be taken at the same time each day, and which caused problems if she missed a dose. I was also lucky in that the local district nursing service were willing to visit elderly and vulnerable people to administer medication, and once the dementia got worse, they visited my mum twice each day, which was really really reassuring. I know not many district nursing services do this, but it might be worth exploring for your mum if it would be relevant.
I do really feel for you - my mum's decline was such a difficult and distressing period in my life, and I felt so helpless for much of the time.