Chook is underweight

[Banksia_the_lorikeet]

Iv got a little bantam hen who is badly underweight, her combs pale an flopped and shes not eating much just seems to sit in a corner instead of being with the other chooks.
Her vent seems to be clean, and she ate an drank bit, their water is mixed with apple cider an garlic, an she was happy to try and get out of my hands , it's incredibly hot here so that might hv something to do with it?
Any idea what it could be? Or how to help her?
I also hv a sweet little rooster with a dirty vent(iv cleaned it as much as I could) an a slightly pale comb not flopped though, he's not as energetic as usual and feeding the hens

 

[Eggcessive]

How old are your chickens? What do you feed them? Does the hen lay eggs? I would offer some form of electrolytes in the water or given orally. Two flat teaspoonfuls of sugar and a pinch of salt may be added to a liter of water to make electrolytes. B complex vitamins, nutritional yeast, or chopped liver may help appetite.

 

[Banksia_the_lorikeet]

Their both nearly two years old, they get scrap,s a seed mix an layer pellets, unsure if she's laying at the moment considering she's with other hens, she never laid much in the first place,
I'll try Ur suggestions thankyou