Is she still lethargic?
What does her poop look like?
How does her crop feel - any odor to her breath?
A change in feed can sometimes upset production, but being lethargic is concerning. It's not completely unusual for a hen to lay an egg while roosting, sometimes the egg laying cycle rolls around at the wrong time.
Check her crop when she goes to bed, then first thing in the morning before she eats/drinks to see that it is emptying properly. She may benefit from some extra poultry vitamins for a few days - you can direct dose her with something like Poultry Nutri-Drench at 1cc per 3lbs one time a day. If you feel she needs a jump in calcium you can give her 1/2tablet of calcium (Caltrate or store brand) for about a week to see if she improves.
Keep her hydrated, dehydration and lack of calcium can cause egg laying difficulties.
If you have a vet - take in a fresh poop sample for testing of worms and coccidiosis overload.
Keep us posted.