Any age bird can get and die from Marek's, not just young birds.Really glad she's doing good!! What's her exact age
Marek's really affects young chickens
Like in 5-6 months of age ..once they crossed their 1 year successfully without any Marek's symptoms or any new birds add in their coop then they have a good immunity n health ..
Give her some essential vitamins and amino acids orally ( not mixed in water)