My mom (age 60) stg 4 colon cancer survivor. Struggling a week with foggy head, disorientation, confusion, unsteadiness walking...Antibiotic for sinus?

Consult her oncologi. Her oncologist needs to know about this new development. Cancer can spread to brain and cause symptoms like the ones you have described. It can also be due to metabolic derangements which can occur due to her cancer. So an urgent visit and further evaluation is advised.