Peggy and Tina were vaccinated for Marek's when they were chicks, because it's highly contagious. Unfortunately, it was too late to do the same for Lisa. My guess is that she and Jackie were exposed at the feed store, but I can't say that for certain.
We were sad to say goodbye to good old Lisa, our remaining original chicken, but I think it's probably for the best. She had grown very thin and frail in the last month, although overall she handled the illness much better than Jackie. Some chickens can even survive Marek's, but I guess that wasn't Lisa's fate.
Here she is enjoying a nice free range in the back yard last summer.
We'll miss her and her big crazy clucks.