First of all,
Lots of things can make chickens lethargic, including mites/lice, worms, infection, or other type of disease. Its good that you've treated her for mites, as they can only add to her weakness. If possible, the next thing I would do is worm her. Some good chicken wormers (not all necessarily sold for poultry, but commonly used all the same) include Valbazen, SafeGuard, and the Worminator. You could also use Wazine, but that only kills roundworms and should be followed by another wormer. Most wormers can usually be found at a livestock supply store, and, if you choose to use it, you can order the Worminator from here:
http://www.twincitypoultrysupplies.com/store/index.php?main_page=product_info&products_id=584
Also, I would isolate your sick hen in a warm, clean place away from other birds. Not only will this keep her more stress free (and therefore strengthen her immune system), but it will help keep the other chickens safe from any disease she may have. Put some poultry vitamins/electrolytes in her water, along with some probiotics. Or you can give her plain yogurt instead of probiotics. Encourage her to eat by feeding whatever she likes, bread, moistened feed, scrambled eggs, etc. It is important that she begin getting nourishment, or she will get even weaker. Greenish droppings are a classic sign of a bird that is not eating enough. If she does not begin eating enough on her own, you may have to begin tube feeding or otherwise force feeding her. Here are two links on the topic:
https://www.backyardchickens.com/t/...h-my-bird-pics-for-visuals-very-detailed-post
https://www.backyardchickens.com/t/722041/how-to-t-feed-a-sick-chicken-and-give-subcutaneous-fluid
It is certainly possible that she has impacted crop. Try getting her to drink some olive oil, or continue giving bread soaked in oil. Massage her crop gently, and don't let her eat any more grainy or fiberous foods, like grain or grass. In many cases, these measures will cause the impacted crop to go away; if not, another way to solve this problem is to perform surgery on the crop. Hopefully, though, you don't have to do that.
Along with those things, look carefully over her body for injury, and check her nostrils for discharge. See if her eyes are cloudy/misshapen at all, and listen for any strange sounds when she breathes. Also, how old is she? If less than 5-6 months, Coccidiosis could be the problem. The treatment for that would be 9.6% Corid (amprol) liquid or 20% Corid powder. If she seems to have an infected wound or respiratory disease, antibiotics would be the treatment.
Hope I've helped!
