Welcome, @Eisbrecher and @WolfTheSpiderDrone!
@WolfTheSpiderDrone, I would become familiar with Khan Academy and its resources for studying for the SAT/PSAT. Although some kids naturally do better on the ACT over the SAT (and vice versa), the reason why I emphasize the SAT is because students who take the PSAT in the fall of their junior year are then eligible to be considered for National Merit status. And there are schools that will offer full tuition or full rides (including room & board) for students who become National Merit Semi-Finalists (based on test scores) or Finalists (which most do, but includes getting a qualifying SAT score to confirm the PSAT score).
Since your parents are unschooling and may be reluctant to help pay for college costs, having options for free or a low-cost education is definitely something I would look into. This thread has additional information you may want to read through.
If you find that the ACT does come much more naturally than the SAT, there are schools that will provide auto merit to high ACT scores as well.
@Eisbrecher, good luck in supporting your niece. One thing you can do to help is to convince her parents how important it is to have a transcript with grades. Most auto scholarships I’ve seen will depend on both a test score AND a GPA.