。
She dialed the wrong number.
Literal
She [topic-は] mistaken number [target-に] phone [object-を] hung.
間違った is the past-tense of 間違う ('to be wrong') used attributively — 'a number that was mistaken,' i.e. 'a wrong number.' Japanese routinely uses past-tense forms inside noun-modifying positions to describe a state that has occurred, even when English would prefer a non-past adjective. 電話をかける ('to make a phone call') is a fixed verb-noun collocation: かける ('hang / put on') pairs idiomatically with 電話, dating from the era when calls were physically connected at switchboards. Other phone actions get other verbs (電話に出る 'answer', 電話を切る 'hang up') — knowing which verb pairs with which is the kind of collocation that takes time to internalize.