。
She went on a trip last week.
Literal
She [topic-は] last-week trip [for-に] headed-out.
出かける means 'to go out' or 'to head out' — more casual and everyday than 出発する (to depart). While 出発する implies a formal or planned departure, 出かける is the natural word for leaving the house for any purpose, from running errands to taking a vacation.