Any way you can get your friend in touch with @Leihamarie? She's dealing with Mystery Ailment with her birds right now. Plus she's lost birds to Marek's so she knows it's on her property.
Back to spreading composted horse manure. Yum yum! The birds are digging it. Literally. :-/
Chickens are so funny - any dirt we dump or dig while gardening is open invitation to "help" us gardening!
Most birds have been exposed to a lot of latent viruses like Marek's, Mycoplasma G & S, respiratory CRD viruses, even AI in it's un-mutated form but hardy healthy birds have good immune systems to fight off succumbing to any of the symptoms of these viruses. I have one Silkie that is predisposed to CRD issues yet the other birds don't display symtoms. We've beefed up her immunity w/ supplemental nutrients and vitamins plus monitor her closely during inclement weather which seems to bring on the symptoms. So far this year she has been issue-free. I lost 2 birds in the last 6 yrs to Marek's -- one was shipped to me by a breeder w/ the juvenile bird already infected and vet had to put her down, a 2-mo chick shipped to me was already infected and died w/Marek's yet her sister was fine and lived healthy up to 3-yrs until heat stress compromised her immunity and she got Marek's symptoms and was put down - the vet who worked in the poultry industry said milder cases the birds can recover so he doesn't euthanize birds immediately - and every time I leave his office he stresses to give vitamins to all the chickens. All my flock has been exposed to one kind of virus or another so I have to assume they are carriers but have been healthy from our vet's diligence to keep them that way. I researched a few years ago that 95-98% of USA backyard flocks are CRD/MG/MS carriers but never exhibit symptoms because of hardy immune systems. That's why I will extra-supplement chickens w/ Poly-Vi-Sol no-iron vitamin drop to brooding, injured, molting, or ill chickens to supplement during times of compromised immune systems.
I supplement w/ a lot of nutrients like very very very trace dusting of Selenium, Brewer's Yeast, Bee Pollen, Rooster Booster vitamins into cooked organic brown rice, children's no-iron Poly-Vi-Sol drop on the side of the beak 2 to 3x week for brooding, ill, injured, molting birds, I use natural Selenium foods like Spinach, Blueberries, etc. Plus offer different types of feed like organic Scratch & Peck layer no gmo/no soy/no corn, organic layer pellets, rolled oats, 3-grain scratch, wild bird seed, raw sunflower seeds (winter) and fresh or canned corn (more in winter). Calcium Carbonite as well as Oyster Shell at-will. We offer cut-up dark salad greens, cantaloupe, grapes, raisins, mealworms, cooked or canned meats (no onions), etc, and they openly forage for bugs and worms in the yard.
As for the acquaintance who claims she has a Marek's treatment, I will have to contact her since she does not post on BYC - she once said she's too busy with her farm to be on social medias and I don't always hear back from her immediately when I text her. She also treats Bumblefoot and does surgeries herself. A real self-made flock vet. She does have a vet for issues she can't handle herself or to obtain the proper diagnoses or medicines prescribed - otherwise she does it all herself.
If they got Dominiques from Cackle near me, I'll let you know! I met a Dominique only once and she was a little love bug 
