You said you used the standard poultry wormer at the feedstore to worm with. That's probably your problem. The standard poultry wormer is Wazine and it *only kills roundworms. Not gapeworms, threadworms or any of the other dangerous worms chickens get. You need to find some Valbazen (albendazole) or Phenbendazole (Safeguard horse wormer) and worm with that. I can't find Valbazen aroulnd here but Safeguard is everywhere. Safeguard kills all the worms with the exception of tapes. Valbazen kills all including tapes. It most certainly sounds like she's got worms and if you used Wazine you did NOT properly deworm her. It's not your fault, I've even seen forum moderators who didn't know. Safeguard will be easiest to find, give ALL the chickens a couple of big pea sized drops of it and repeat 10 days later. Or better yet, repeat with the Valbazen 10 days later. you'll probably have to order it online though. Chickens can and will die from worms and it can easily seriously stunt their growth.
Edit: Ivomec is worthless for worms but does work well for mites and lice.