It would be good to get a weight on her. You can weight yourself while holding her, then subtract your weight from that number to get a rough weight. Kitchen scales are good to weigh chickens as well. With the SafeGuard for 6 pound hen you would give 1.5 ml (0.25 ml per pound.)
Welcome to BYC. It can be hard to know what type of problem they have with wheezing, whether it is a respiratory disease or what. Infectious bronchitis, the most common one, can cause fairly mild symptoms, such as sneezing, and some nasal or chest congestion. But it also can cause problems with...