How to prevent sinus infection?

Hello doctor,

I am writing this on behalf of my wife. She is 26 years old. The problem is that she is prone to sinusitis. She gets infected with sinusitis at least once in two months. When she gets infected, it takes one to two weeks to recover. Her nasal passages gets blocked and she finds it difficult to breath through the nose. Also, the mucus is very thick and she tries very hard to squeeze the mucus out. Sometimes, she applies too much pressure and finds blood stains in the mucus. She tried vaporizer and saline spray, but none of them seems to work for her. She also gets a severe headache at times due to the mucus getting blocked. She feels a pain around her eyes too. Due to this she remains inactive during the entire period. The assumption is that most of the time, she gets infected due to exposure to dust or cold climate. Is there a permanent solution for this problem? Is there anything that she can do to prevent the infection? Please help.