HAHAHAHAHAHAHAHAYes you can have the vet check their stools for parasites.
I think it is more likely she is molting. Can you pick her up and feel her pelvis? If you feel for her "hip bones" for lack of a better word, if you can fit 1 or 2 fingers between them she is not laying. If you can fit 3-4 fingers there she is laying. There are some diagrams on this website, not the best but I didn't see any better at a quick glance. http://www.small-farm-permaculture-and-sustainable-living.com/buying_chickens.html
Also if her vent looks moist she is laying, if it looks dry she is not. Again there are plenty of web pictures if you do a search. Just be careful how you word it or you may get a few surprise pictures.![]()
A few days ago I got excited about a naked neck and looked up 'naked chicks'....yeah, that backfired...

On the pelvic bone check, if she's started laying but has stopped, say due to molt, will the space close up or once its spread, does it stay that way?
Of course its now silly cold today so even if she were laying she'll probably take today off.