One of the chickens not growing well and is now limping

[Palls123]

I bought it from a hatcher who vaccinated against Mareks. Could it still be the cause?

 

[Wyorp Rock]

I bought it from a hatchet who vaccinated against Mareks. Could it still be the cause?

Yes, unfortunately Marek's could still be the cause even if she's vaccinated.

What's her poop like?
Is her crop empty in the morning before she eats/drinks?

I would keep her separated but near the others. Ensure that she's able to stay warm.
Do your best to encourage her to eat/drink.