Most likely something happened to her that caused some kind of fear.
My younger one also had some rough “childhood”. History is, he got into my car, the bottom of it inside the protective plastics. I was at work and couldn’t for the hell of it remove the cat. So I had to drive home, where with the help of my brother I lifted the car and had to remove those plastics to be able to rescue him. (I drove 40km with him scared always meowing, rough ride).
Took him right away to a vet to see if there was something he needed care with, had just a burn in his tail which I got medicine for.
Nowadays he’s scared very easily and hate visits. Though he’s the sweetest cat, even allows me to pet his belly. But that’s why I guessed that he already had some history.