Leave this baby some food, water, a soft bed in a covered/hidden/'secure' place, and leave the door to upstairs open during the day in case she wants to investigate. I'll bet you'll find that she eats. If you will try canned/wet food instead of just dry (wet has more protein, which cats need), you will also be better able to tell if she is eating it.
Good luck with this poor traumatized little one.
Jan in VA