There really are no “leftover scholarships”. Schools spend a lot of time and money on enrollment management and have longitudinal data on what they need to reach targets. This includes scholarships offers and the yield from these offers. They already know how many students will take them up on the offer. The school will always extend more scholarship offers that there will be people who accept. It is the same as the school already knowing that not every student they offer admissions to will arrive on campus in the fall.
Remember Auburn does not guarantee scholarships based on GPA and Grades
If your D has already committed to Auburn, what is the incentive to offer her more $?
Trust and believe that Montevallo has to work a little harder to get high caliber students than Auburn. If it is about chasing the dollars, you can still change your mind, have your D withdraw her decision to attend Auburn and follow the money at Montevallo.