Hi, and welcome to this forum.
I am so sorry that your Mother has ALS, but hope you can find some help here, sometimes it helps just to talk to other people who are going through the same things as you.
I am not an expert at all, but I have attended some seminars about communication. I have bulbar ALS and can't speak. I still have good use of my hands, so I write most everything on a small whiteboard and also use a communications device that is like a little computer.
For your mother, maybe just an alphabet display -the ahphabet printed out on a board or paper that your mother could point to with her left hand to spell the words. Or, sometimes if she could point to just the first letter of the word to give a clue, you could understand the rest of the word if she spoke it.
Also, maybe a board made up with phrases or things that she would say often, like, "I am cold", "I am in pain" "Please bring my glasses" or whatever would be suitable for her.
Do you have the services of a Speech/Language Therapist in your area? They might have some other ideas of things to help your mother.
I know there are devices that are controlled with eye movement and things like that, but they are hi-tec and you would need a therapist to talk about them.
Hope this helps and I pray that your mother gets something to help her communicate better.
Leah