Any chance that you can take her to a different doctor. Maybe tell her it's for a second opinion (well, it is....really).
My Mom suffered from Alzheimer's and I remember all too well the early days of forgetfulness and confusion. It was hard on her because she had enough wits about her to
know that something was happening. When we'd tell her that she'd just repeated herself she would get flustered and I think that made it worse. But....it's hard to ignore.
Maybe if you could find a doctor that could get her on one of the new Alzheimer's meds it might help.
It's a tough diagnosis to hear. But researchers have developed more treatments than they had when my Mom was dx with it. I hope you can convince your family to get another opinion.