Working with a very sick deaf patient also with dementia. i am caretaker who can't sign. to make her more comfortable

Well the best you can do is try to learn, or if she can read lips, then try to talk slow or make sure she's watching.
In terms of making her more comfortable, just repeat what you always do. if there's something she enjoys like certain activities, then recreate them each day.

I don't mean to sound condescending, but learning sign language isn't that hard, there are a lot of tutorials out there, and although they're just the basics, I'm sure she'd be happy that you're giving the attempt to communicate.
If you do try, remember that it takes time to get the hang of it, So don't stress or give up.

Talk in soft comforting voices and try to help her relax by juse softly petting her head and brushing her hair massage her soulders and try to alwys smile at her no matter what but dont make it seem too fake.
and mosrt important DONT LET HER FEEL LIKE YOU ARE FEELING BAD FOR HER

Ibelieve the answer is c) our brain jumps to conclusions based on past experience