Does she have flu?
A) yes, almost definitely
Correct.
The fever, runny nose, dry non-productive cough and malaise are consistent with, but not pathognomonic or flu. However, the sudden onset of profound malaise is almost pathogonomic for flu. It occurs in a small percentage of cases, but when it occurs during flu season, the diagnosis is almost certainly flu.
The differential diagnosis of a young woman with these symptoms includes respiratory virus (e.g. rhinovirus, respiratory syncytial virus, adenovirus), atypical pneumonia (e.g. Mycoplasma/pneumoniae, Chlamydia pneumoniae), bronchitis (usually has purulent sputum), and sinusitis with post-nasal discharge (usually no systemic symptoms).