Oh no, my first chicken emergency! Not sure what to do.

Woke up today and went outside to let the hens out of their coop. One of our chickens was unable to get out of the coop by herself so I lifted her out. Turns out she can't stand, can't walk, acts drunk/dizzy and keeps falling over. No balance at all.

She's looked crappy lately but I thought that was just because she was molting. Otherwise she's been fine, just scruffy looking. She is right about one year old and I do not know if they were vaccinated against Mareks- never even occured to me to ask the person from whom I got them.

Any suggestions? We're pretty new to chickens so I have no idea what I should do.

Edited to add: We've removed her from the rest of the flock and have her in a dog crate for now. She ate a small cup of yogurt with no problem this morning and is now eating some feed mixed with some BOSS. She also seems to have no trouble drinking.