I can't remember how old she is but have you tested her for hearworm? Coughing is a sign of heartworm, but *usually* not until it is in a more advanced stage, *usually* 1-3 years after they are infected. But better safe than sorry.

Other than that everyone else has said what I would of. Kennel cough would be my first guess, followed by an obstruction of some sort, then heartworm or other heart/respiratory problems.

She is such a cutie. I hope she feels better soon!