I would probably go ahead and treat for worms with Safeguard paste or one that gets most chicken worms, not just roundworms. I would look at her vent area for any lice or mite activity. You can check her vent for an egg with a rubber glove and lubricant. Check her crop first thing in the morning to make sure it is empty and not impacted or sour. Many chickens suffer from internal laying, and about all you can do is look at everything and rule out one thing at a time. Hensinthe HOUse has a good recommendation to observe poops fro a day or so--the color and consistancy can tell you a lot about things like worms, blackhead, and E.coli. It's easy enough to put her in a cage in the coop overnight.