There are a several reasons for a dog to cough. I will give you some information on cough in dogs.
1) Kennel cough is a very common reason. Sometimes vets will prescribe a children's cough suppressant like Robitussin DM to help with the coughing and an antibiotic, but if this is Kennel Cough it can last as long as 2 weeks and then resolve itself.
Treatment for tonight until you can see the vet in the AM.
You can try taking your baby into the bathroom and steam it up. This way the steam may help the congestion. Keep her in the bathroom for at least 20 minutes. To help relieve the congestion. You can also open a jar of Vicks Vapor Rub in the room where it is out of reach. That should also help.
2) Internal parasites can also cause coughing. Round worms and Heart Worms are the biggest offenders. Round Worms can be found in a stool sample, where as Heart Worms have to be tested via blood work. If your baby is not on a Monthly Heart Worm treatment, it would be very wise to have him checked for Heart Worms. http://www.thepetcenter.com/gen/hw.html
There is also the possibility of a Heart Problem that can cause a dog to cough, gag, and wheeze. If this is possibility it would be best to get your baby into the vet ASAP.
She may also have the beginnings of URI. This can happen with the crazy weather we have been having this year. The vet will have to administer proper medications after an thorough examination of heart and lungs.
Allergies can also cause a cough. Plain Benadryl, at 1-2 mgs per pound of body weight every 12 hours can help with aid with an allergic reaction.
Here is a site that talks about coughing in dogs.
This link is for Robitussin DM.
Please follow up with your vet in the am, since this is only basic first aid.