My mom was told her they suspect a brain tumor&won't find out until tuesday. would they say brain tumor if they weren't pretty certain already?

Hard to say: Often tests are ordered to "rule out" or "on suspicion of" so that insurance will pay. That is different from a Dr. telling a pt. that he/she truly suspects a certain diagnosis. BTW, in a radiology report "suspicious for" is a little more certain than "consistent with" and much less certain than "diagnostic of". Also all brain tumors are not alike, some are completely curable.