The description of your mothers symptoms points towards acute sinusitis.
Sinusitis is in general viral in origin,
Next Steps
Steam inhalation 2 -3 times a day, sipping warm water, paracetamol or ibuprofen, mucosolvan to aid thinnig of mucus, plus otrivin nasal spray
Health Tips
if the symptoms gets worse with ,fever suspect that it is bacterial sinusitis which needs antibiotic