Could be any number of things.

Post-nasal-drip due to allergic rhinitis, a bacterial or viral sinusitis. Or possibly broncospasm due to virus, allergy, ...

Really hard to tell without observation, more information.

FYI - our son's dairy allergies were anaphylactic but he tested negative for several years.

With a family history of allergy, it's likely that asthma and/or allergies could develop. If it continues and your pediatrician cannot diagnose, consider taking her to an allergist.

Certainly, your ped should rule out any treatable bacterial trigger.

If the sinuses are chronically involved, you may end up needing some kind of preventative treatment.

Our son's allergic profile made his nasal passages inflamed. Any virus would trigger a sinus infection, then a nasty asthma attack, even on asthma preventatives. When we started him on nasal steroid sprays, his asthma attacks pretty much stopped.

Hope that helps.

Mark