One of my girls used to cower at live and f/t even if they were smaller than her. She would only eat if I left her alone with them overnight in complete darkness.

I would try turning the lights (or at least hers) completely off and see if that makes a difference. If not, I would try mice or asfs if you can find them. I wouldn't go to the vet until exhausting more options imo since that's going to be extremely stressful for her.