。
She raised her hand to flag down the bus.
Literal
She [topic-は] bus [subject-が] stop [so that-ように] hand [object-を] raised.
~ように attached to a non-volitional dictionary-form verb expresses purpose: 'so that X happens.' The key contrast is with ~ために, which requires the same actor in both clauses for a volitional purpose ('I did Y in order to do X myself'); ~ように accepts a different subject in the subordinate clause, often a non-volitional verb (止まる, 分かる, 聞こえる). Here, she does the raising, but the bus is what should stop — different actors, so ~ように is the natural choice. Flagging down a bus this way is standard practice in Japan: at all but the busiest urban stops, drivers will only pull over if they see someone clearly raise a hand.