I'd have her checked out by a vet.
It could be the KC returning, or heartworms (although coughing in heartworm is usually only common in advanced stages which usually takes 2-5 years but you never know).
It could be just from excitment especially since her throat may be irritated from having the KC, or maybe she eats too fast or a combination of factors.
It could be something more serious like a heart condition or cancer of some sort or the like. The possibilites could be endless and since it happens at all different times under different circumstances it would be best to have it checked out by your vet.

Good luck!