What are some words of comfort for someone who has come to see their own mortality and is scared?

As many know, my 84 year old mother has dementia. She also just spent about two weeks in the hospital for several problems associated with old age. She is in a rehab center now but this last crisis has caused her to begin to realize that we are only immortal for a limited time.
She has seen her own parents, her husband and several sibling pass away over the years not to mention many friends but this time the hospitalization shook her up. She is scared. Scared of death, scared of dying, scared of the unknown, scared that it may happen at any moment.

She has never been a very religious person and so the thought of soon being with God or “going home” is of no comfort. I find it hard to say things like “Death is no more than passing from one room into another ” or “Soon you will be with dad again” or similarly pointless phrases that seem to comfort many of the faithful. The second is particularly uncomfortable since she has never fully acknowledge my fathers death, even though he died in her arms, preferring to believe he ran off with another woman rather than accept that he is gone.

I am looking for things that might comfort her, if only for a short time because with her dementia she may forget what concerns her in the here and now but the fear will return over and over again and each time it will terrify her.

Anyone have any suggestions?