Is she drinking the water frequently? Does she drink like crazy or just sip? (in comparison to the others)
Also, how old is she? How often is she laying? How is her feces? Any yellow in it?
Pale combs can be anything from dire (if there are other symptoms) to just nothing at all. It could be the start of something, or maybe she's just old & isn't laying much anymore. So the more info we can get, the better. Please keep up with the updates. And for sure update if there's any blue tint in the comb.
I think protein would be fine to give her. You can give her cooked egg yolks back to her. Either hardboil or scramble them in coconut oil (good for birds). Bugs are a good source of protein. So is beef heart/liver if you've a butcher nearby. Yogurt is always good for a source of probiotics which can help digestion. Probiotics (yogurt, acidophilius, kefir) can help replenish a gut with good bacteria.
Also, you said you checked for mites, but have you looked for lice around the vent area? (a telltale sign of lice is a type of 'buildup' of grey at the base of the feathers where they meet the skin.) Worms in the stool?
Have you checked the roost area for mites? Put a butter knife inbetween the cracks of wood & see if any 'blood' comes out. If so, you have mites feeding on the birds while they sleep & hiding during the day.
Another thing, is she acting broody at all? Sitting in the nest more than usual?
(Sorry for all the questions, but again it helps!)
