R..
It is called the 100 day cough for a reason it lasts about three months. I looked at the CDC vax schedule and it states as follows:
Diphtheria, Tetanus, and Pertussis Vaccines
There are several formulations of vaccines used to prevent diphtheria, tetanus and pertussis. Some are combined with vaccines to prevent other diseases and reduce the total number of shots that someone receives at one office visit. In the U.S., DTaP, Tdap, and Td vaccines are most commonly used.
Children should get 5 doses of DTaP, one dose at each of the following ages: 2, 4, 6, and 15 through 18 months and 4 through 6 years.
So if she was only vaccinated as an infant it sounds like she might be behind on her vaccination schedule.
I would follow up and make sure she is covered for other childhood diseases and if once you have whooping cough does it give life long immunity.
So be kind to yourself try and relax...drink fluids...and know it will pass.