。
She was chosen out of many students.
Literal
She [topic-は] many [genitive-の] students [genitive-の] inside [from-から] was-chosen.
の中から ('out of, from among') uses the locative 中 ('inside') with the source-of-motion から — 'from inside the group of students.' Common with selection verbs (選ぶ, 選ばれる). 選ばれた is the past passive — 'was chosen,' since the subject is the chosen one. The whole construction is a variant of the partitive 'out of N' pattern.