There is no guarantee for the future. And, she can always make higher payments (snowball). That is what is saving the interest—paying them off quicker.
Helen
P.S. I speak from experience. My hubby and I were making good money–I changed my student loans to higher payments. Then, I lost my very secure teaching job—and got behind. It took me forever to straighten it out. Had I kept the payments smaller—we could have made the monthly payment during the job loss and not had to worry about it.