transfer to BYU and get in as a transfer student. Me, and all 7 of my siblings did that and got into BYU no problem. Lived at freshman housing as well.
Don’t even have to take the ACT. Just skip senior year. Waste of time, academically at least. Other factors such as friends and social environment may be factors to consider, but it seems that’s not important already if she wants to leave early for BYU anyways.