Not roosting, breathing seems labored

[Porch Chickens]

My orpington, lemon, stopped roosting several weeks ago and is sleeping in a nesting box. Doesn't appear broody but also sitting a lot during the day and strangely enough she prefers to sit almost in the waterer, so I'm assuming she must feel very thirsty to want to be that close to it. She's just get up and walk around but seems to have low energy and her breathing seems labored with her tail moving up and down with each breath. She is still eating and drinking. Other than her stop in roosting, I only noticed these symptoms yesterday. I actually found her sister dead in the coop yesterday morning as if she had passed away in her sleep. I hadn't noticed any odd symptoms with that one but it made me take a closer look at lemon. I can't hear any wheezing, but we did have our Americana, Rue, about two months ago (I posted about her here) who was wheezing terribly and I thought was going to die. I gave that one a course of Baytril and she is now good as new. I've ordered another bottle of Baytril for this one and hoping that will help her.