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

Try listening to some Alan Watts recordings on youtube. I have a similar attitude toward death as he does, but he can articulate it much better.

She has never been a very religious person and so the thought of soon being with God or “going home” is of no comfort.
Is she an atheist? There is no telling how to even fathom something to say without knowing what she thinks happen after death. 

I really don’t know @rojo and I feel sad for you and her as you work through this. All I can think of is to celebrate her life rather than focusing on death. Get out the photos, the videos, the books, films and music that have meaning and connect to her and your life. Get a recorder of some type and when she is lucid ask her to share her memories. Hopefully, you can distract her fear of the future by focusing on the past.

@Hypocrisy_Central No, she is not an atheist. She was raised Catholic but left the church when they refused to accept my C of E father. Her mother was devout but while most of her siblings continued to attend, church was not a big part of their life.

And perhaps at this point thoughts of God might bring her comfort.

And thank you for pointing out I need to find out what her thoughts on what happens after we die.

First, my heart goes out to you. Any time there is a shift in personality of someone you love, it can be devistating. I’ve been there.

What you need to know is that dementia requires constant surveillance. While there may be times of lucidity, it will only get worse over time. Currently, there is no cure. This means that preparations need to be made now, if they already haven’t been made for her to live in a secure environment. She may live for many more years before dying of natural causes or another reason.

What you need to understand about dementia is that the thought process has changed. It won’t be what you are used to. What is very important is that you adapt to their her needs that bring her happiness and security. This may include saying statements that you do not believe.

The worst part is letting her go when then the time does. If you have medical and/or religious qualified people in involved in guiding you through the process, it is easier.

This is also the hard part. Did your mother document what her final wishes are? If so, it’s time to have them on hand. If not, now is the time to talk to her about it when she is lucid.

Oh how sad @rojo. I remember my own father being afraid of death too.

I believe when we die, no matter what our belief is we simply change form. All of us are vibrant entities, that surpass the physical body. For example, fire becomes ash. Wood can become a fire, water can become ice and ice can become water.

I strongly feel we become a part of something bigger. The universe, call it what you may.

We spring forth from our bodies and join other entities that form the energy that keeps earth spinning and moving, but in more profound ways than that.

There is so much evidence of life after death and also reincarnation. We never die, we simply change form. Perhaps she might enjoy these ideas, that is why I shared them. I feel so heart sore for her. Perhaps you can ask a counsellor to talk to her about her fears?

I’m sorry for your troubles dear @rojo. Are there hospice care nurses looking after her who you could talk to about this? They will have experience of this situation and I’m sure will have good advice.

@Stinley up until the rehab she has been living with my sister. She has home health coming in a couple of times a week and physical therapy when necessary. My sister and brother are talking about her fears and needs at this point. Better late than never I guess.

@rojo I don’t know how it works in your area/country but is there a local hospice you could contact, just for this advice. I’m positive they would be sympathetic and helpful and may offer a listening or counselling type service for your mum or you.

I haven’t read the other answers so I hope I’m not repeating anything.
One, I would acknowledge her fear and anxiety. I would give her hugs.
Practically I would ask her doctor about anxiety meds. Is she on hospice or just recovering from illnesses? If she’s on hospice the meds are probably already prescribed so you can talk to the nurses when you notice her bring over anxious and they’ll give it to her. If not, and you can talk to her doctor I would mention her anxiety and ask for a prescription.
Depending on the dynamics of your relationship, you can use frankincense oil mixed with coconut oil and rub it on her temples and her feet. It really helps to reduce anxiety. My experience with using it with my mom was that it created a sacred space without having to even have a spiritual discussion. I know that might sound woo woo and would not be appropriate for all relationships but I’m throwing it out there because it was so meaningful in our family.