I would check on what kind of dental work she has done - root canals on top teeth typically spread infection to sinuses and its almost impossible to eliminate it with Antibiotics since blood flow to the site is reduced or eliminated.
Also check for specific food allergies (blood type, ayurvedic, metabolic typing and other could shed some light on that).
Personally I have used Colloidal Silver on my sinuses with some sucess (still have root canal so all it does is keep it under control). If its fungal infection than perhaps a grapefruitseed extract dilution or even a weak peroxide solution could know it out. Always check for underlying issues before just trying to treat the focal infection first.
Mike