I need help understanding this

Welcome. Sorry you need to be here. She will probably never accept that she has dementia. This is called anosognosia and is pretty common. It is the inability (her brain can’t) to recognize her symptoms or limitations. It is a very difficult symptom to deal with. We hav a saying here, never try to reason with a person with dementia. It will only cause you both to become upset. I will attach the dbat staging tool. You may notice it actually gives a rough age equivalence at each stage. They are aging in reverse. The thing is you never know when she will lose that next skill. This makes it important to stay one step ahead in her level of care. What is her living situation? Living home alone at the stage you are describing is not going to be safe. If you are living with her, with your own medical conditions, this might not be safe for you. Have you looked into a facility. There can be a waiting list to get in some places. Do you have a DPOA? This is very important.
Different ways to approach problems- 1) If it doesn’t matter, she is just always right. Pick you battles. 2) Do what needs to be done without consulting her and sometimes without even telling her. 3) Never try to reason with her. Proof and logic won’t work. Live in her world and stop fighting to bring her back to reality. 4) Use a therapeutic fib. I know it seems wrong, but if a fib will ease her stress and anxiety, in my opinion it’s worth it. 5) Avoid topics that may cause stress and anxiety as much as possible. I would never bring moms house up in conversation. She is very angry I won’t let her live at home. It can be a bit like walking on eggshells. There are a lot of touchy subjects to avoid. 6)Accept that sometimes there is just no safe option that is not going to make her mad. Medication may help.
I will attach some resources.

https://www.helpinghandshomecare.co.uk/care-advice/what-is-show-timing-in-dementia-patients/

https://iona.org/therapeutic-fibs-ok/

Please get educated on this illness. You need to define your role. You'll always be a loving child. Seek guidance, whether spiritual or other, to find acceptance that this is your mom's current situation. Start going through the grieving process as it will be a long one. Your role may also be caregiver. If this is so, you need to allow things to roll off of you. If you are bringing her to the store, act like a professional caregiver. When she complains that you are always on your cellphone, whereas you are just gripping your phone to watch for a call back from her doctor, just say, "you're right mom, I do spend too much time on my phone". If you already feel your health is at risk, pull in the resources right now, e.g., in home care, potential placement, respite, home grocery delivery, or other. Please hang in there.

My mother in some ways is very cognitively astute. She knows she has dementia. Does it help her? No. Does it help me? No. I'm sure it makes her very sad and frustrated. She was always very competent and independent. The intelligent, competent person I knew occasionally makes brief, cameo appearances. They are getting fewer and shorter. I have gotten used to her referring to me as "mother". I am in many ways the parent. We don't have the driving or financial issues to deal with. I set up some of the accounts so I have the passwords. She does not. My mother doesn't drive and I have the debit card. Still it leaves a lot to be desired.

Thanks for listening.