If she is losing feathers...do you see any "Pin feathers"..i.e. spikes...where she has lost feathers ? If so..she is having a moult (molt ) which is perfectly normal...if so..she is unlikely to lay any eggs for some weeks as a moult takes a huge amount of their energy away from them..during...
What product did you use to treat the possible mites problem ?
If you saw mites on her then all of your chickens are likely to be suffering from the same problem...you need to treat ALL of them with Sevin dust or Permethrin...paying special attention to under their wings and the vent areas...