K.C.
Since it's happening at night, try to think about her routine and see if you can spot a cause. Does she take a bath right before bed? Maybe something in her soap or shampoo is affecting her. My son (who does have asthma but had problems even before his formal diagnosis) has definitely come out of the tub wheezing if we use a different soap, and often if he's showering somewhere away from home where we know other soaps are used.
Do you wash her pajamas or sheets in a different detergent? That could be the culprit. Do you use a certain cleaning product in her room? Is there a chance that there is mold in her room and she's allergic to that?
I was also going to suggest anxiety. It's possible that it's now a psychological reaction - since it happens every night, she expects it to happen and probably worries about it happening. As a result, it happens.
Try having her do deep, relaxing breaths (think yoga but without all the poses) and give her something calm to think about. Hopefully by relaxing, the symptoms will go away.