Hello! My name is XXXXX XXXXX it will be my pleasure to help you with your dog today.
Collapsing trachea is actually pretty common in small dogs. I have a maltese cross who has it and has an attack a couple times a week for years with no problems.
This can be a chronic, degenerative issue that could impact the health of the dog. You can find more information on this particular issue here( and although this is an article about small breeds, there are large breeds with this issue as well): http://www.toybreeds.com/health.htm
The other thing I was thinking was the possibility of this being some kind of cardiac cough. Dogs get congestive heart failure (also known as CHF) just like humans. This is when the heart doesn't pump as effectively as it should, which causes fluid to build up in the lungs, making the dog cough.
Tracheal collapse is normally treated with a cough suppressant and steroids, although many vets opt to not treat until the dog is showing a compromised respiratory system, and since your Callie is acting normal otherwise, I'm not sure that there is a problem with the respiratory system here...but it's always better to be safe than sorry.
There's another good site that goes over treatment options here:
If Callie were mine, I'd give my vet a call in the morning and have them take a peek and determine if they think she should be on some medication at this poitn.
I hope this helps!!