My 7 year old daughter was diagnosed with flu. we treated her with tamiflu (oseltamivir) for 5 days and expectorant. after 7 days she'still w/chest congestion...?

Residual cough: She either has a residual cough from the flu or she may have developed bronchitis or pneumonia secondarily. Take her to see your doctor for evaluation and treatment.

Tamiflu (oseltamivir) not a cure: Tamiflu (oseltamivir) suppresses the flu virus but doesn't kill it. The respiratory irritation triggered by the virus will produce changes in mucous production & flow that may result in residual cough that can last a few weeks. If she was getting better but seems to have become sicker now a re-visit is in order. If it's just a lingering cough, i would just watch it.