Mom 85.stroke 3 yrs ago shows no signs of dementia 3 yrs later other than mild forgetfulness rarely and confusion also rare. Does she have dementia?

Mostly likely Early . Decreased vascular blood supply from aging and genetic hardening of the arteries from cholesterol and loss of insulin levels with age ie Early diabetes type two leads to these symptoms which are early mild dementia, also secondary dehydration can ad to these symptoms!
Dementia is a term. widely used (often inaccurately) to describe a number of chronic brain disorders including MULTIPLE small strokes. A single stroke is unlikely to result in this type of "global" dementia.
Hope this is helpful!

Dr Z.