。
She wanted to become a teacher.
Literal
She [topic-は] teacher [into-に] wanted-to-become.
~たい expresses the speaker's desire — 先生になりたい means 'want to become a teacher.' The past form たかった ('wanted to') implies this was an aspiration that may or may not have been realized. The ~たい suffix conjugates like an i-adjective: たい (present), たくない (negative), たかった (past), たくなかった (negative past).