Oh dear! I was so hoping for a photo of her hiding under something and yet feared this is what the post would be about. My heart hurts so badly for you. Does she respond to treats? Have him go outside shaking them. Does she come when called? I'm sure he'll be asking all neighbors and shelters. Does she have a collar on? How far are you away from home? Last year I was two hours away when Aroara wouldn't eat for the catsitter. This was when she had been bitten by the snake. I knew I wouldn't be able to concentrate or sleep. So I drove home and the stinker ate her food as soon as I offered it to her. I had to drive back the two hours the next day. I'm not saying that you should go home, just saying that I understand your dilemma. Please keep us posted and be assured you are certainly in my thoughts.

ETA:
Do you have access to a humane animal trap that he can bait with some really stinky food to lure her inside?