It sounds more like an allergy. Usually colds don't produce too much sneezing. That's usually from an irritant (allergen) in the nasal passages. Same thing with the reverse sneezing; a lot of reverse sneezing is from allergy drainage. Can you call your vet and ask them what the dosage would be for Gigi for benadryl?

Chester weighs about 11 lbs and he takes a 25 mg benadryl twice a day, but you should call your vet since Gig may need less.

I'm sure glad she's not throwing up anymore!