。
She still hasn't finished her homework.
Literal
[topic-は] still homework [object-を] has-not-finished.
終わらせる is the causative form of 終わる ('come to an end, intransitive'), literally 'cause [it] to end' — 'finish [something].' Functionally equivalent to 終える, but with a slightly different feel: 終わらせる emphasizes the active conclusion of an action, while 終える is more neutral. Both work for 'finish homework.' まだ + negative resulting state gives 'still has not finished.' 宿題 ('homework') is one of the iconic words of student life in Japan; school summer vacations often come with formidable summer-homework packets (夏休みの宿題).