I had a deviated septum and had the same operation years ago. At the same time they drained my sinuses and the problem was cured although I don`t know which was most effective - probably the sinus drain.
She could look into possible causes of what aggrevated the sinuses - various theories such as eating dairy products. Or she could have some allergy tests. My sister has dreadful sinus problems and had the same op 30 years ago and it`s only now she`s discovered she`s allergic to grass (not even the pollen - just grass)!