。
She made it in time for the bus.
Literal
She [topic-は] bus [for-に] was-in-time.
間に合う ('to be in time, make it in time') is a fixed expression literally meaning 'fit into the gap/interval' — the gap being the available time before something happens. The に marks the event that has to be made on time. The construction is the positive counterpart of 間に合わない ('miss it, not make it'). Useful across deadlines, trains, meetings, supplies — anywhere 'in time' or 'enough' applies.