If she died of Marek's, she could have picked it up anywhere in transit to you or on your property or from contaminated clothing. I only allow immunized birds on the premises. Mealworms can carry Marek's. You might want to look at the Extension websites for more information and diagnostic help. There is a UCD poultry help hotline number where you can get help diagnosing your chickens, help learning to care for them, and so on; I'll repost it again.
~866-922-BIRD (2473)
Most breeders breed for immunity.
Some will still die from Mareks cancer. The immunization does not stop active mareks.
