Have Cat Questions? Ask a Cat Vet Online.
Do not give children's cold medicine. Most of this stuff is not proven safe for animals, especially cats. If she is breathing very badly, it is best to get her seen now as respiratory issues are not something to mess around with. If you cannot get into a vet, you can try giving her Zyrtec. The dose is 5 mg (1/2 of a 10 mg tablet) once daily.
I hope that helps!