The caliber of teachers in high schools aren't the best. Should more teachers be invested? Of course. But there's a line you don't cross in class.
If I didn't understand orbitals and halogenation after it was taught to me in class, I learned it on my own Your teacher can't go inside your brain and force you to learn anything.
Most learning goes on OUTSIDE of the classroom anyway. The classroom is just the initial source of information. You go home, study your ass off, come back and make the grade.
You do not, however, throw hissy fits in class and expect people to take you seriously.
And if buying self help books is extreme when you don't understand a subject then maybe you're really not serious about passing a class.
Even in college, professors give no f.ucks if you understood what happened in class. You go home with your notes, research, study, ask friends. Do what you need to do to make sure you know what's going on. If she's doing this in high school, she's in for the shock of her life when/if she gets to college. Just saying.