@coach723 has given really good advice so far. Have you tried taking her aside and feeding the egg or cat food to tempt her to eat? Have you given the Poultry Cell or NutriDrench for iron? Is her crop emptying by early morning? Are they getting outside to roam around. Chickens can be weak and puny when molting, and especially if they have a mite infestation. Dusting with permethrin should be done again after 5-7 days, since the eggs hatch that often.
sorry i had forgoten to say that i tried the cat food but she seemed uninterested, my hens have not been laying much due to molting and mites (my ducks at the moment once a week, molting, and they are due an egg any time now so should have one soon)
her crop is almost always empty, i brought her in to a seperate cage in my (car free) carport with a heat lamp on the 20th, i did not need to top up her food once then on the 28th another hen, caramel, was not doing well outside so i brought her in too, she is in the cage with her sister and this morning i had to top the food up (i think caremel was the one who ate it all)
thye normaly live outside in a big pen but since i brought them in they have not been out as it has been horrible weather here in england, really wet and windy and i was worried that dandelion would not cope with that
i am treating them with ivermectin (as a spot on) and spraying their vents with a mite spray
they have had 2 treatments of ivermectin so far, a week a part (i am planning on doing 3 treatments)
she is really weak and just sits under the heat lamp and stumbles when i touch her
i have access to a bird vet if needed