There are a few reasons that can cause a dog to cough. Each one may require veterinary treatment to help your dog overcome the cough.
Kennel cough is a very common reason. Sometimes veterinarians prescribe a children's cough suppressant to help with the coughing and sometimes even an antibiotic, but it usually goes away on its own in about 2 weeks. You can try to allow your dog into a steam filled bathroom at 15 minute intervals to help give her some relief.
Internal parasites can also cause coughing. Roundworm and heartworm are the biggest offenders. Roundworm can be tested with a fecal sample where as heartworm is detected through a blood test. If your baby is not on a monthly heartworm treatment, then the risk is very elevated that she could have heartworm.
There are also heart conditions that can cause a dog to cough and wheeze...if you feel this is could be a problem the sooner your get your baby to the vet, the better. :)
She may also be starting an upper respiratory infection or may even have allergies causing the issue. If you think it might be allergies, you can try plain benadryl, providing you are not giving her any other medications. 1-2mg per pound of body weight every 8 hours to aid with allergies. :)
Some dogs can have reactions to Hartz flea drops, so this is a bit more concerning to me as she is having some breathing problems along with the coughing.
Go ahead and your vet a call or ER vet and have your baby checked out and bring a fresh fecal sample with your for testing. You can read more about canine coughs here:
You can read about the use of Robitussin here:
I am sorry to not be able to pinpoint exactly what is going on, but those are some reasons this could be going on.
Good luck and hope she feels better soon :)