Neck stretching

[jersey bean]

I'm back! We had a sick chicken who kept doing this funny diagonal neck stretch, looked miserable, and her crop seemed enlarged so we took her to the vet (being newbies) and he agreed about the crop, washed out her crop and found nothing untoward and gave her an antibiotic shot.

Two weeks later she is much perkier, but is still doing the neck thing. We got all our hens at the same time, from the same place, all Bovan Goldline, they have all been treated exactly the same.

Is it just a behavioural quirk? When they 'croon' she sounds more like a foghorn....

Any ideas?? I'm stumped.