Any advice for dealing with my Mom's anger?

I am living with my 87 year old mother -- she could not live here by herself, and we get along just fine 90% of the time. Her health is not the best, she is a type 3 Diabetic, and heavily medicated but she can get around on a walker. I have attended support groups for caregivers (she bathes and washes herself, but I cook and consider myself a caregiver). I think she is in the beginning stages of dementia and perhaps has some short-term memory issues but by no means is she an Alzheimer's sufferer now. She does see a psychiatrist once a month.
My main problem with her is her anger. She argues with many people loudly, and for inappropropriate reasons. She always has had an assertive personality but her verbal outbursts now -- at myself, my sisters on occasion, neighbors, and people in movie theaters is difficult for me to deal with.
When I drive, my mother can start arguing with me for not listening to her and driving the wrong way, even though I am right. She can be so loud I worry about having a car accident. We had an argument last week, and I had to tell her to stay quiet because she was distracting me and I was worried about a car accident. She did, and later on she said to me "driving with you have brought back all the bad memories of living with your father (he is deceased and their marriage was not that great). You are just ,like him".
My mother can be sharp and tell me to shut up out of the clear blue, and take offense to things that I can't figure out. Just now, we had a bad argument and I cannot really figure out why. She bellowed at me at the table and i had to leave. But the loudness of her voice can be upsetting to me.
Here is my issue in a nutshell. The situation living with her is fine 90% of the time. I think we have both gained coping mechanisms for dealing with each other. But how do I protect myself when she picks a loud fight, starts bellowing at me, raising her voice and making a scene, for a reason that does not make sense to me? And is there anything I can do to avoid any triggers that set her off? I just want peace.
My worry about my mother is that in four years time she is going to be in some facility and will turn into one of these people who is bellowing and yelling and severely angry at just about everyone for no reason at all-- and there is nothing I can do about it. What I have to worry about personally is not having a personal health crisis as I help the mother whom i love live out her years. I do feel like her punching bag right now and there is nothing i can do about it. .