Chicken can't stand up and walk, please help

Hi guys, I got a new chicken from one of our family members, she was like this already when we bought her, but we know she wasn't like this before. we thought we could save her.

So I'm doing all I can to help her, I'm scared it might be mareks 😭 she ate earlier, but she keeps panting even though she is well ventilated,

I've been giving her multivitamins for the past day, I just keep hoping she gets better ❤️ what are your thoughts on this? Please help me thank you in advance 😁