Denial is huge. My Mom has been dx'd with dementia, but both of my parents were in denial. We tried to get homecare, etc. for them to no avail. They kept saying they were fine.
I finally told my Dad that he would need to come to us when he decided they needed more care. Finally he did that just a couple of weeks ago. He told me that my Mom is wearing him out because she misplaces things all the time. My Mom who was the sweetest being on earth has become irritable. I think it's because she knows that things are not normal for her and it must be tough not being able to remember events, where you put things, etc. I also had to put my foot down about doctor appts. I told them that I needed to be with. I explained to the doctor when we went in that I needed to represent my Mom, and she agreed. I signed a power of attorney form so I can access her online doctor's records/appointments. Take care and good luck with your Mom.