Mom won't accept the fact that she has dementia. Any advice?

When we have taken our mother to the doctor for her regular check-ups, the doctor would concur when my sister would ask if mom has dementia or alzheimers. Mom would immediately deny this blaming a seniors moment - mom is 80 -or take the fifth and not offer any other explanations. Mom has steadily gone down hill the past 4 years. That was when she was given an ID card instead of a drivers license. Also at that time she washaving her cataracts removed due to her eyes going bad. She steadfastly told her eye doctor that she was going to beat the macular degeneration. Now a days she does not see much better than before though she no longer wears her glasses. She does little reading and listen to the tv rather than watch. When I visit her in the memory care facility I am greeted wth teary eyes and open arms. I know that in time she will definately need to be in this or another facility but I believe that as long as mom has the fight in her she should be in her comfort zone and be in her own familiar home. I was her caregiver prior to her going to the facility and would be the primary caregiver if she went home - with support. My sister is the p.o.a. for mom so she is the one that mom and I would have to convince. Any chance of bringing mom home home - even for a short time ? any thoughts or ideas ?