Sick hen

I have a hen I just got the night before last that is not moving as much as the others, and her breathing is somewhat labored. Her butt is flexing as she breathes. I assumed she was egg bound, so she’s in a warm epsom salt bath currently, but then noticed her breathing is a little…raspy? I’m worried it may be something respiratory. She’ll be quarantined from the rest of the flock. What else can I do?