My 9 month old baby has terrible flu with a runny nose. which over the counter medication is suitable for her because her doctor is fully booked?

None: If it is truly flu your options are limited. Infants that young may be given prescribed antivirals if in a hospital, but the potential side effects limit their use to the most severe cases. The main focus is on fluid balance & easily digested nutrition. If they can pee every 6 hrs or more they have basic fluid needs met.

Nasal saline/Zarbees: Nasal saline and infant Zarbees are available. In addition, cool air mist may relieve cough and congestion. A viral illness tends to have a duration of around 10 days. If there are fever spikes, worsening symptoms or poor feeding, please see your pediatrician.