She's a carrier for life, unfortunately, and the other birds have already been exposed. Just wait for someone with a mareks flock to give you advice. It's not a death sentence but you will have to change your management
Diotomaeceous Earth does nothing to mites or lice.
Can you get permethrine based powder or spray?
What's their diet?
How old are they? Are they molting?
How big is their space for how many birds?