Bevel, loved your suggestions about approaching your mom when she is in a good mood and just trying again later if she is not receptive the first time.
I did want to comment on one thing you said about your mom. There is no such thing as "old age dementia of some sort which is normal of people in her age group". While over 50% of people over 85 develop dementia, that does not make it "normal"! She might have Mild Cognitive Impairment or the doctor may be saying that she has some form of early stage dementia but he is not sure which one. Also, an MRI is only one of many tools used for diagnosing dementias, as they are diagnosed by exclusion and rule out. Excuse me, please, if I am being to emphatic or difficult about this, but my father was told some time ago he had "normal aging related dementia" which confused him and all of us, and we lost about 18 months of time when we were making the wrong assumptions about the care he would need, the cost of that care, and the appropriate medical treatment. I am not trying to discourage you but I feel angry when doctors minimize dementia symptoms this way. I can tell you are very caring and sensitive to your mom, and are doing a good job taking care of her.