I would bring her inside to a dog crate with food and water so that you could observe her. How old is she? Have you added any new birds recently? Does she have any nasal drainage or bubbles in her eye? Have you ever had a chicken who had similar symptoms before?
The only diseases that have similar symptoms to what you’re describing could be Infectious Bronchitis Virus (IBV), Infectious Laryngotracheitis Virus (ILTV) or even Aspergillosis. Just keep in mind that ILTV is incurable and there’s no treatment for it. IBV can cause permanent reproductive system damage for life, making her more lay little to none as well as making her prone to becoming egg bound, get lash egg (salpingitis) and even egg peritonitis. Eggs will also often come out as wrinkly, soft or thin shelled, loss of pigmentation, misshapen or roughened. Aspergillosis isn’t contagious, however, but other chickens in the same area can inhale the spores, causing similar symptoms. Anti-fungal medications will help, but the spores will only remain dormant until your bird get sick with another illness or if she gets stressed.