It would not hurt to give her a dose of human calcium citrate plus d3 vitamin incase she is having a tough time getting ready to lay her first egg. About 300-600 mg. Straight into her beak, pull her wattles down gently and pop the pill in her mouth. It sounds like she was showing interest in laying and was hanging out around the nesting box. She may be having a tough go round. The calcium boost plus d3 could help with contractions.
I’d be shocked if she was sick with coccidiosis at her age. Usually they build up immunity to the soil around them by her age, but it’s always good to keep an open mind.
Let me tag some others and see what ideas they have
@Wyorp Rock @Eggcessive
Keep giving her supportive care until she snaps out of it or we can find out what’s wrong. Sometimes after a deworming, if they’ve had a heavy worm load they can feel puny.