Lethargic hen has iritated skin

[Hens rule]

Cupcake my 5 yr old bufforp lost one of her best friends a few weeks ago, the day after easter. She has acted sad after this and when i went out to my hens at 11 am she was still in the roosting area sitting where she sleeps. I checked her crop its empty her abdomen feels normal to me. She has mites all under her feathers and alot on her butt and belly area. The skin around her butt is red maybe from the mites? The last week or so iv seen weird poop around i think its cupcakes. Its a light green with little circles and diarea ill get a pick. Whats wrong with cupcake?