。
She didn't have to come to the meeting.
Literal
She [topic-は] that meeting [to-に] come necessity [topic-は] did-not-exist [but-のに].
~必要はない ('don't need to') uses は as a contrastive marker on 必要 ('necessity'), highlighting 'as for necessity, there wasn't any'. The trailing のに ('despite / even though') colors the whole sentence with regret or wistfulness: 'she didn't have to come, and yet [she did, or yet here we are dealing with the consequences]'. Japanese leaves the second clause unfinished; the listener fills in what hangs in the air. This kind of dangling のに at sentence end is a classic spoken-Japanese expressive device for unspoken complaint or resignation.