@californiaa, “most kids that take AP Physics had studied physics before. Probably, for several years already. In some after-school programs, online, with tutors, or prep classes.”
I have to respond to this. No, I don’t believe that “most” or even more than a very tiny percentage of kids who take AP physics have been studying physics for several years, in after-school programs (we barely even have physics classes around here, I’ve never heard of such thing as an after-school physics program), online, with tutors–no, most students do not have tutors, or prep classes (huh?–again, never heard of such a thing as a physics “prep class”). The OP did nothing wrong by having her son simply enroll in physics. That’s what most kids do. There is no huge lead-up with years of prep, studying, tutoring as you state to enroll in high school AP physics. Usually a prior year of high school physics if it’s AP physics C. In some schools a prior year for the defunct Physics B, and in some schools not. That’s all.
"I suggest my D to study physics and chemistry at least 2 years before school, “at home”. Then she is sufficiently prepared to take double AP Chemistry/ AP Physics in one year. " I see. Yet on this site you have stated a thousand times the tired refrain that all that is necessary to be successful in school is to do your homework. Evidently that, and making your child spend two years studying on her own before enrolling in the class. And evidently you believe that taking extensive prep classes outside of school, having private tutors, etc, is the usual practice from your comment above. So which is it, just do your homework and all will be fine, or bring on years of prep classes and private tutors so that you already know all the material before the course even starts?