I hate DE, consider ineffective and also a harm to the respiratory system.To treat for that I've started dusting her with DE and putting 3 drops of Ivermectin on her skin.
She and her flock-mates eat layer/starter feed pellets
Ivermectin is a cattle dewormer that works on many things but is VERY harsh on the system and NOT approved for use in poultry in addition to being pricey. What made you go with that choice?
Permethrin spray is by far the easiest and very affordable thing to treat with.. but the Ivomec might already have hit hard and heavy so I don't know if you need to treat again or not.
@ 7 weeks old, LAYER feed is completely inappropriate and should be eliminated and avoided until eggs start. The lower protein (16%) doesn't adequately support their growing bodies and can cause delayed development. While the excess calcium (4% ish) can also stunt growth, delay laying, AND *possibly* (doesn't mean will) cause kidney failure if fed long term to birds not in lay.
Mixed veggies is a fine TREAT but NOT good nutrition and not what I would give to an ailing bird. The trouble breathing was not caused by pain or those bloody spots. It was very likely something respiratory that was allowed to proliferate by the immune system due to the added stress of the lice, the move, and so on being a bit overwhelming. It's great that you are seeing improvement. That's what happens when you get things under control and the immune system starts fighting the good fight.