Advice needed for poorly buff oprington!

Hi all,
Just wondering if anyone could give me some advice? I have a 3 year old buff Orpington. She is eating well, laying fine and in general pretty much seems to be herself during the day but is now having quite a problem with her breathing when she goes to bed. Her breathing is slightly more noticeable during the day but the moment she goes up to bed and sits down her tail starts to go up and down and she has to open her beak. She has no eye or nasal discharge but instead of snuggling down with her friend like she always used to she now sits alone just trying to get as much air in as possible, she also feels much hotter. She's already had a course of antibiotics incase it was infection and I've wormed her. She lives in an omlet eglu which I keep nice and clean and I recently removed the bedding incase that could be irritating her. I took her to the vet again today who wasn't sure what the problem is but gave her a steroid injection to see if it would help but tonight she actually seems worse. Any ideas of what it could be would be really appreciated, she's a much loved pet and I don't like to see her struggling.
Thanks