For severe asthma. Azithromycin has been shown not only to kill atypical bacteria which makes asthma worse, but also reduce inflammation. Small studies which examine the effect of Azithromycin on improving asthma are conflicting. Therefore, the best use of Azithromycin is for severe asthma patients who aren't controlled on standard asthma therapies on a trial basis.
Some Research. There has been some research that has shown a link between late onset (after puberty) of asthma and certain bacterial infections. The best advise would be to get checked out by an allergist to see if this could possible be the case. Their research showed improvement with 6 weeks of antibiotics in a small group of patients.
She may need inhaler. Call your wife's doctor, and speak to them about her situation. Let them know that the tablets are not working. See if they can offer her an inhaler, that might help her breathe easier. Also, look at her diet to make sure she's off dairy as that can produce more phlegm, until her symptoms abate. Make sure to check for food allergies.
See your doctor. Bronchoconstriction may not be caused by bacteria, and therefore would not be improved with antibiotics.