I absolutely think you are dealing with mold. Brain fog and fatigue are telltale signs. Her sinus problems are also indicative - she may be able to get over them more easily due to less exposure. And yes, your mattress is probably to blame. There are so many more toxic molds beyond Candida.
I highly recommend this formulation for helping your body get rid of mold and heal from the mycotoxins they leave behind. It was developed by a very skilled healer, Cofe. I've interviewed him and he knows his stuff. He combines the best of Science with traditional healing. He has reams of patients who have seen their lives turned around thanks to his formulations.