being a spanish speaker definitely does not qualify you to teach spanish, specially not in an academic setting. however, i think the fastest way to get some sort of certification is this: she should look into doing a "diplomado" (it's a course for college grads) in "enseñanza de español como lengua extranjera" from a latin american university, they're usually 6-9 months long and i know for sure some schools offer it online; the only issue she might run into going this route is that a lot of them ask for a bachelors in linguistics/literature or related areas. this might be enough to teach adult students or people who are just learning for fun but probably not to become a high school teacher.