How "easy" should the freshman course load be?

^this is what my D did/plans to do. She sat down and plotted out 8 semesters of study to see if she could double in two STEM areas and still minor in Spanish. She also wants to study abroad spring of junior year and do at least one summer internship. It appeared doable on paper and she is moving along quite fine now finishing up semester #4, rising junior. She takes 5 classes/18 credits per semester ( generally three at 4 cr and 2 at 3 cr) if she can, a balance of sorts. It is important to take the classes in a particular order and to boot she is at a relatively small LAC that offers some classes only spring of odd years or fall of even years, that sort of thing, which just complicates things. She has completed all requirements for one major and nearly all for the Spanish minor, hopefully she’ll have a more relaxing study abroad semester and take a couple humanity/diversity type classes.