。
She missed the bus.
Literal
She [topic-は] bus [for-に] was-late.
~に遅れる ('be late for X') marks the missed event with に — the bus is the target, the thing she failed to be there in time for. Compare 'be late' meanings: 遅れる describes failing to make a deadline or appointment; 遅刻する is the more formal version typically used for being late to school or work. The English 'miss the bus' compresses what Japanese expands into 'be late for the bus.'