@urbannarnia27 from my experience with mites and lice, I learned that it is best to clean the coop out as well. Have you got Sevin Dust? Mix some of that with enough water to make a milky solution and spray this mixture all over the coop, nest boxes, every nook and cranny. A vet friend gave me that tip some years ago and it's very effective. The thing is, no matter how well and clean you keep your coop, it just takes one infested wild bird to visit long enough to start a problem. Or in my case, my MIL's CATS! They had fleas, they hung around the coop, next moment… It happens.
The shell-less less, if your hen is broody I'm guessing she's not laying, so the young pullets could be the producers here then… although if they all had bugs, that could well be it? Either way, if it's due to lack of experience or bugs, the problem is manageable with time and bug treatment and curable then with the addition of some oyster shell offered free choice, alongside their regular feed and a splash of ACV (apple cider vinegar) in their drinking water for a week will help with nutrient absorption and egg production as well. *Note: give this in a plastic waterer as it corrodes metal*