The only thing you can do to confirm worms if they are not yet presenting in the poop is have a fecal float test done by the vet. I would isolate this chicken so that you can check her crop in the am (before she’s had anything to eat or drink) and so that you can get a fecal sample that you are...
Is she napping with her feathers all puffed out, lethargic and eyes closed?
Have you checked her crop in the morning to make sure it completely empties at night?
Any sneezing / wheezing : rattled breathing?
Did your vet do a fecal float test for worms?