Pullet having breathing issues

This pullet has had a few issues for last month. First i thought i witness her having siezures, then more recently i noticed she sometimes has very labored breathing like she's opening her mouth very wide and sticking her tongue out. She eats and drinks with the others, her appetite hasn't gone away at all. But now she also has a limp, i don't know what is wrong with her, it seems like everything that can go wrong is going wrong all at once with this chicken. Please help

 

I can take a video tomorrow. No, none of my chickens are vaccinated

 

Before the seizures she never shown any symptoms. It was like she'd thrash around uncontrollably before calming down and getting back up and going about her business. It only happened twice of what I've seen. She doesn't drag the leg, she holds it up. She tries to put pressure on it and was able to get up onto the roost to sleep.

 

Its been raining and the temperature has been dropping. Its dry in the coops, clean no mold. I was thinking respiratory but she doesn't have a runny nose, sneezing or any swelling

 

So an update, i noticed her sneezing this morning. I also noticed her still trying to use the leg but holding it up. She doesn't look sickly yet, she's still trying to part of the group and her appetite is still strong. I'm thinking i should get some kind of med to treat this if it is a respiratory infection.

 

An update, I'm very scared that what she has is indeed mareks. the leg she was holding up is now out in front of her and she definitely can't move it anymore. She isn't dragging either of her wings. And she still has an appetite and she still takes very deep breaths. I was planning on moving birds from her flock to my larger flock but now I'm scared too in case mareks is what she has