I'm sorry to hear this. My dad has a little bit of dementia. He was diagnosed with colon cancer summer 2018 and the resulting surgery that Fall pushed him over the edge. The doctor told us that usually it starts coming on with a patient and they learn to compensate and cope with it in their normal life but then a big medical event occurs and pushes them over the edge. Dad has gotten a bit better over time as he healed from his surgery and gotten into better physical shape due to living in a nursing home and being taken care of by he onsite medical staff but every once in a while I'll be over there and he'll ask about the whereabouts of his long dead sister or daughter and I have to remind him that they've been gone for many years. Anyway, I hope things go well for your mother and she finds some peace with it. All the best to you...