How Often Should I Worm My Chickens??

My chickens, Black Australorps, are one year old. Last November I wormed them all with Wazine, followed up 2 weeks later with Safeguard. 

However for the last month I have a girl who's comb is turning more and more pale by the week. She is not quite as lively as the others, however she is the lowest ranking bird so I can not tell if she is hanging back because of illness or just her position in the group. She has no other symptoms of anything. Poop is completely normal. She is a good layer and lays nearly everyday. 

She eats like a horse and in the morning, there is VERY little poop under her end of the roost bar. 

We had a VERY dry winter although it was a cold winter, getting below zero a few times. Very little to if any moisture. I run a clean operation and keep the poop picked up and the coop clean as possible. I checked her for mites and did not see anything at her vent, behind the neck or anywhere else on her body.

Could this bird need to be wormed again?? None of the others are showing any signs of pale combs. And none of them, including the pale comb girl have any diarrhea. Could she have some other internal issue?? She did have a spell last winter with yellow urates and stopped eating and I had her on antibiotics, which got her back on her feet. 

Should I worm her?? Thanks!!

Thanks so much! I have gone over her several times this past week and can not find any external parasites or signs of them anywhere. Her crop moves just fine, I give it a feel in the mornings when there is little poop under her butt. But the crop is empty. I have checked it before bed and it is full.

She has had no injuries, no limping, feet issues, she acts normal, she eats well. Just this pale comb thing. She looks a bit tired. 

Thank you for the info on the fecal samples. I will have to gather some up and take them to the vet. Thanks!