Background: The character in question was kidnapped at age four from a small chain of islands in what would be our Pacific. She was a house slave until the age of eleven, when she is found and freed via the legal system. She is extremely intelligent for her age, but is somewhat stunted educationally from not having any formal education. She only went to a public school once in her life, when her owner wanted to throw off the authorities by making her look adopted, at about 4th grade.
1: Her island country has its own unique language that she has been speaking for longer than she's been speaking English. Would she be able to retain any basic knowledge of the language--such as a few idioms, sparse vocabulary, and some childish terms--and be able to pick it back up later if she began to speak it with someone older than her who speaks fluently?
2: Could she self teach herself anything after her stint in public school? things like basic math and reading--nothing complex. I'm hoping she could work herself to a passable 5th or 6th grade level.
3: How would she be tested to determine what grade she should be placed in, if at all? Just basic comphrehension tests or what?