OK, an acre away works too, if you have chicks.
Generally speaking, chickens don't get colds. They can have dust allergies or get mild respiratory infections, but it's extremely rare. Ninety-nine times out of a hundred when you're seeing sneezing and coughing, it's the result of infectious respiratory disease.
My recommendation would be to contact your local avian veterinarian and have her blood tested, starting with the tests for Mycoplasmas gallisepticum and synoviae. They are by and large the most common cause of infectious respiratory disease. Blood tests are the only way to confirm for certain what you are dealing with. If she comes back positive (likely), she will need to be humanely culled, as there are no cures for Myco or most other infectious respiratory diseases, only treatments; once they are in a flock, they are there for life.
I would suggest not attempting to treat her at all until you get the blood tests done, as any medications might interfere with the results.