How do I convince my mother she is in need of additional help than just me?

Well, you can't 'convince' a dementia patient of anything, really, because they're way beyond the point of comprehension. Everything is about 'them', what they want, when and how they want it, and nobody else exists. My mother, for instance, wants one of the residents kicked out of her Memory Care community b/c he gets on her nerves. If I were to ask her if SHE should get kicked out of there should SHE get on someone else's nerves, she would say no, or the question would fly right over her head.

Some people have to go through the school of hard knocks before they understand they need more help. Or a walker. Or a wheelchair. Or a visit to the doctor. Or or or.

Your mother may have to hurt herself and take a trip to the hospital & then go to rehab where they will refuse to release her back to independent living in order to 'understand' or to accept the fact that she is now disabled. At that point, you will have to make alternate arrangements for her care; ie: Assisted Living/Skilled Nursing/In home care-givers, etc.

In the meantime, she'll go about her merry way feeling like she needs nobody's help for anything until a crisis happens. That's what happened with my father, and I had to place both of them in Assisted Living.

Good luck!

Do you mean her cognitive testing is very low, meaning that she has dementia? Is she at risk of harm due to not having proper supervision for her medication, food preparation, hygiene, etc.? If so, I'd not continue trying to convince her. Often, seniors are not able to process the information, see things clearly, etc. I'd either just do it, if you have the authority, or if you don't have DPOA or Healthcare POA, seek a consult with an Elder Law attorney about what evidence you need, the process, etc. At least you'll know what evidence you need and to go about it. If she's not there yet, at least you'll be able to say that you tried. It might help to get her help with doctors for all the mental health issues. They may be able to prescribe help. Is her doctor aware of exactly what her needs are, if you didn't step in? If she can't take care of herself and her household, then, someone should be able to intervene, although, she may never see it that way.

I have the same. 79-yo Mom doesn’t think she needs help, but last hospital visit neuro/psych drs say she is just short of incompetent. Sent home with home nursing/PT/OT which is almost finished. Still doesn’t think she needs help, even to have something called
Telehealth, where she is set up at home with daily monitoring. She’s not interested because she thinks after home care is completed, she can go back to normal.

I feel for you, me and all caregivers who care for dementia sufferers AND who have been stubborn all their lives.

If your mother has dementia, she is beyond the realm of "rational thought" as in "oh, my daughter can't do all this for me, I need to be more considerate of her time constraints and health".

Mentally, she has become ego centric and only concerned with what she wants.

Therefore, you need to say "no, Mom, I can't possibly do that". You can't convince her. She is not going to agree. You just have to say "no".

I also think telling her that it is you that needs help might work.
But if she is paranoid that might be more difficult.
Is there an Adult Day Care that she could participate in? This would give you a break, her a break.
A "friend" (aka caregiver) could be introduced and the friend could stay with her while you are working. This way she will not be alone and if she is alright alone now in a month, or more, or less she might not be. Ya just never know.
I think introducing the caregiver as a friend might make it easier for her to accept

Boundaries. If there is dementia involved, and there may very well be, forget about convincing or reasoning with her. You need to set boundaries with her. What are you willing and able to do? Many people do not like extra people in their homes, much less so strangers.

You could try telling her YOU NEED the help and time for yourself and get the help, and leave it at that. The help is not for her it is for you. Some have luck taking that tact.