Sickly RIR hen, pls help!

[Plant_Hoarder]

Hello, I've been noticing issues with my roughly 3 year old RIR hen. I'm not sure when it started exactly, but she has had a poopy but for about a week or two now I believe. I didn't think much of it since we've had some heat, but very recently she has developed other symptoms. She is panting, and today it is quite cool, in fact, she is the only chicken of mine that is panting. Also, her feet appear to be facing inward, and he is waddling very close to the ground with her butt hanging the lowest. She moves around with the flock but tends to pick a spot and lie down. She's been eating and drinking thankfully! I do not know when she last laid an egg, nor have I satred her on any treatment yet, I just don't know where to start! None of my other poulry has shown any symptoms. Any and all input is appreciated, thank you EDIT: Just had to out her in the coop because she's so freakishly heavy that I'm assuming is weighed her down.. She was not overweight before.

 

[SmiYa0126]

Hmm, I think I would dose her with calcium citrate. How's her crop at night? How's her poop? Do you have aqua mox on hand? Heavy breathing could be a sign of infection. How's her bottom compare to another hens bottom, is it same size or bigger, of bigger she may have ascites. I haven't treated a hen for that but there is an article on this site in the learning section under diseases.