I would probably take her in for my own peace of mind, if it were me.
But I did want to ask for clarification: Is she "whooping" when she inhales, or is she "barking" when she is coughing (exhale)? There is a difference. Whooping is also not the same thing as wheezing (which can be asthma).
Whooping is on the inhale at the end of a coughing fit; wheezing is the sound when exhaling through narrowed airways, and barking is the exhalation/coughing through inflamed voicebox or upper trachea.
Barking does sound JUST LIKE a seal (and that's a sign of croup). If she is making noises when trying to inhale, then I would take her in.
http://kidshealth.org/parent/general/eyes/childs_cough.html
(Sorry to keep adding.. but wanted to clarify. Just making noises during the inhalation doesn't mean that it is pertussis. It could also be stridor, which is difficulty inhaling due to swollen trachea or larynx. And that needs treatment ASAP. When she inhales, if the muscles/skin across her ribs or neck pull in, then that is something you need to take seriously.
My son had croup every winter until he was about 5 years old. It can be scary. But mostly happens at night (the barky cough). Thankfully, as bad as his bark was, he did not develop stridor and didn't need any emergency treatment. Cold night air works well for croup. We never had any luck with steamy bathrooms.
Re-reading your post, you indicated that she is making the noise at the end of a coughing fits and on the inhale. I would take her in.)