。
She must be home by nine at the latest.
Literal
She [topic-は] late at-most nine-o'clock [by-には] return-home must-not-not.
~ねばならない is a formal/literary variant of ~なければならない ('must'). 遅くとも ('at the latest') sets the upper time bound. 帰宅する ('to return home') is more formal than 帰る. The combination of ~ねばならない and 帰宅する gives this sentence a strict, formal tone — like a rule imposed by a parent or institution.