Please help, what should I do?

My mother can be controlling, and until I was in my late 20s I'd never spoken back to her. I was reserved when I was younger and she'd say I was mousey/had no gumption.She always referred to me as being "a bit slow" and "dense." I was often called "a tit in a trance".

All is well if I ignore her put downs and and sarcasm, which is what I mostly do but there are times when I crack and we argue, sometimes going nc for weeks. It's always me that patches things up, and if I feel I've been wrong l apologise. Mother never apologises.

Things came to a head the other day when I went to accompany her to the bank, she's in her 80s and needed some help. I also got her shopping. This was the first time I'd seen her since well before Christmas, she lives 25 miles away.
She became angry and shouted at me because she didn't like the advice I was trying to offer. I was extremely embarrassed as there were people in the bank, most of who were now looking our way.
Once outside it kicked off big time because I told her she had embarrassed me.
I still got her shopping while she waited in the car, and when I joined her in the car she acted as though nothing happened.

I am seriously thinking of going nc with her, but don't know if I can do it. I think I'd feel guilty because of her age. Has anyone else found themselves in this position and gone nc with their mother?