Why does sister talk about mom's "dementia" when she never had tests for this?

Dementia: Your sister may be noticing things like episodes of forgetfulness, repeating the same story multiple times, or declining ability to do daily activities. It's important that your mother have a thorough neuropsychiatric evaluation to see if any of these changes might be from reversible causes (such as thyroid disease, certain kinds of anemia, liver dysfunction, or medication side effects, etc).