Another tutor here, just wanted to point out that both the ACT and SAT recently cancelled the essay section, so there’s actually no need to prepare for that – yay for shorter tests!
I’d tailor your approach to your daughter’s learning style. Does she have the discipline & persistence to get the basics by working her way through a test-prep book on her own? Or will she need the structure of a class, or the encouragement of a private tutor? Honestly, the prep books+Khan Academy are pretty good. If she’s a motivated visual/verbal learner, she can probably learn half of what she needs to know, or more, from reading and working through a book for about 12-15 hours – long enough to get exposure, but not so long she gets discouraged or overwhelmed. Then, she could work with a tutor to learn & practice the remaining half over about 5 months with ~1.5 hrs tutoring + 1hr homework per week.
But if she’d benefit from having external structure & direction from the get-go, I’d recommend starting with a tutor right away. With her relatively high baseline, I just don’t think a basic group prep class will add as much value because it won’t be tailored to her specific needs.
This summer is a great window to dedicate some study time before junior year ramps up, and to hone her overall reading/skimming skills – the ACT Reading & Science require speed-reading. On the other hand, her math knowledge will improve significantly as junior year goes on, so she will want to either make an effort to learn the handful of advanced concepts ‘early’, or wait for a spring test date. My 2 cents – interested to hear what others think too!