Not eating

I was here two weeks ago, when our isa brown was poorly.  She got a little better, but has now gone downhill again.  She is eating very little.  I have tried her pellets mashed down with water, but she is not very interested.  She will take wet bread, which I combine with the pellet mix, but not sure if that is all that good for her.  I have drained her crop twice in the last two days.   She tends to just stand around, all fluffed up in a ball I guess fighting the cold.  Her black rock mate is fighting fit.
Any ideas?

Sour crop is terrible and the outcome is not always good. You could take her to the vet for treatment with antifungals and then antibiotics, or to be put to sleep if she's suffering