I wonder is she could hatch the eggs under the broody, vax the chicks when hatched (herself or a vet if not), then keep mama and chicks inside away from the main herd, for 10 days. To let the vax take effect. By then the chicks would be ready for outside anyways.I took the chance. I do not have proven mareks in my flock. It was a "possibility" mentioned in Legertha's necropsy report. I did not get vaccinated eggs rather I took a chance. It seems to have played out fine as Aster seems to be doing well but make no mistake, it was a risk.
Since Legertha was vaccinated for mareks I considered it an acceptable risk. @RoyalChick knows there is mareks in her flock and has to act accordingly.
Just a thought…