Good post JinHamasaki.
The only contention I want to make is the reason for her quitting school. No one knows for sure except Ayumi herself, but the impression I got from the interviews I read was that her being "slow" and her deep voice was more of a problem in her elementary school days, not when she actually quit school. At the time she quit, she had already gotten into modeling and immediately moved to Tokyo after quitting. Once in Tokyo she did enter high school, but only briefly and quit again. I think by that point she had pretty much decided that she was going to be in some kind of entertainment field and school just wasn't going to be any use to her.
edited to add: We could do a whole analysis of Ayumi's psyche. hahaha.