Atelectasis in my 15 month old

My 15 month old daughter, who was born 2 months premature, has had ongoing atalectasis, first in her left lung now in both.  She has only had 1 clear x-ray in 15 months.  Cystic Fibrosis has been ruled out by a DNA test, but we still don't know the root cause.  She has been on daily breathing treatments (2 times daily, sometimes up to 5) of Xopanex and Pulmacort, sometimes with Acetylcysteine solution, USP depending on how rapid her breathing is.  Everything I see on the internet about atalectasis centers around surgery or plugs causing the problem, but this does not apply in our case.
Other than this problem she is a healthy baby, other than very slow weight gain (she is only 17 pounds).  The only sign she gives for her lung issue is her rapid breathing.  
So, exaclty what questions do I need to ask her Pediatric Pulmonologist so we can work towards finding the root cause?  I really am at a loss, as we thought we had this thing taken care of a few months ago, and it just showed up again in an x-ray a few weeks ago.

Thanks,
sean

[National Jewish]

I would discuss possible causes with this physician and if asthma is the problem now.  Seeing this specialist is a good idea to get to the bottom of the problem.