Chicks don't usually sicken and die suddenly from Marek's. I would guess her problem was she was bullied away from food and water and she became too weak to fight her way to the feeder.
I'm so sorry you lost her. Try not to blame yourself. It's simply not possible to know every thing about chickens, and you really did do the exact best thing by giving her Gatoraid.
You'll get past your grief in time, and this will stick with you as a learning experience. Next time you see a weak chicken, and if there are no other symptoms, the first thing you do is to give a sugar/electrolyte solution which can restore glucose and electrolyte levels. This will often revive a chicken that is suffering from hypothermia, dehydration, and starvation, all with similar symptoms.
I'm so sorry you lost her. Try not to blame yourself. It's simply not possible to know every thing about chickens, and you really did do the exact best thing by giving her Gatoraid.
You'll get past your grief in time, and this will stick with you as a learning experience. Next time you see a weak chicken, and if there are no other symptoms, the first thing you do is to give a sugar/electrolyte solution which can restore glucose and electrolyte levels. This will often revive a chicken that is suffering from hypothermia, dehydration, and starvation, all with similar symptoms.