Golden Comet hen losing weight, droopy, pale comb...

[S Curry]

I just noticed one of my Golden Comet hens feel really light, and seems to be a bit mopey. She was hatched in mid March of this year and been a great layer and a sweetie as well. I have some Tylan 50 as well as some other medicines laying around. Her eyes and nose etc. are fine. I haven't seen her poop so I'm not sure, but I haven't seen any diarrhea around the coop.
ANY SUGGESTIONS APPRECIATED!
Thanks!

 

[S Curry]

Also, her vent seems fine...