How old is she? Do you have a flock and do they free range at all? Have you wormed the flock? When, with what? Repeated?
What do they eat? Have you examined her all over? How is her crop? Is she eating and drinking on her own? Do you know how to do the "Q-Tip test for Gapeworms"...
Chickens occasionally "gape", especially if they are eating mash or if you make a wet mash of their food.. but, with the wheezing, it would be good to rule out gapeworm.. it is a harder worm to treat and can and will kill a chicken. (Sorry)...
So.. get some regular people Q-tips.. hold her.. lift up her head a bit to stretch out her neck some.. pry open her beak.. and hold on to the Q-tip very well.. do not let it slip from your fingers.. reach down and back .. (avoid the airway, avoid the little windpipe hole).. swab her throat... reach as far down as you can (which won't be too far, q-tips are short)... swab around.. pull it out and look at it.. if you see worms.. she has gapeworm.. I have heard some say that if you see blood they have gapeworm, but I am not sure of that..
Search for (here on BYC, using the Search option)... search for "worming", "worming with Valbazen", "giving oral medications", "dosages of Valbazen"..... look for posts by dawg53 on worming.
If she is sick, has a Repiratory Infection, then any and all of your flock can and will get sick also. The Duramycin 10... most of the time I give 1 tsp per gallon of water that they will drink in 24 hours, taking away any other sources of water.. some here say to give more than 1 tsp... to give 1 1/2 tsp per gallon.. change it everyday or whenever it turns dark or gets dirty.. keep it fresh. I would give it to the whole flock for three to five days.. if you think she is sick. Give it to her until she has no more symptoms for a couple of days.. or consider worming if you haven't.
Worms can cause symptoms that make you think the chickens are sick.... sick with an illness, when really they are sick from worms or parasites. (Also, have ou checked her for mites? Looked at her vent and under her wings ("armpit skin") to see if there are any mites on her?
Best of luck.. lots of good info here if you use the Search. Hope she gets well..