I do think you should interact with her, though. Pick her up, listen to her breathing... does it sound funny? Check for a respiratory issue. I took my chick that was self-isolating to the vet. Can you do that?
That crouching down behavior worries me... I’ve seen it twice before in chicks that ultimately didn’t make it. I have no feedback but will follow along to see what other, more experienced chicken keepers have to say.