I have a 3 year old hen who hasn't been eating. Each time she reaches down to eat, she appears to vomit up white fluid. She seems now to have no appetite, but will roost at night. No injuries present; she's standing up good, just appears tired, won't walk around much. She also appears to maybe getting ready for a molt, I was thinking this was related, until I saw here vomit. My guess is some sort of illness that might pass. We've isolated her, and put her under a heat lamp, because it recently got cold. I tried to give her some egg to eat, she tried it briefly, then wouldn't eat it. Advice appreciated.