Stanford or Harvard is basically hopeless.
It is difficult for IGCSE to study in the United States, but it still depends on which school you want to go to, Stanford or Harvard. It's basically impossible, but if you really want to go, you can still take some internal training courses at Stanford, but you still have to get TOFEL or s at scores, otherwise it's still impossible.
Professional consultation of overseas study institutions
If you want to go to a general university, you can consult the staff of some professional study abroad institutions. After all, I dare not jump to conclusions. Finally, I suggest that you consult professionals in overseas institutions before considering whether to go to college or high school in the United States.
Opportunity does not apply.
The daughter of the guardian of the other friend, I think she must have some other documents or some experiences appreciated by others before she was admitted. This is accidental to some extent, but it is not applicable.
California schools are adaptable.
America is safe and can rest assured. If you are afraid of not adapting, you can try to apply to a school in California. There are many Chinese in San Francisco, California.