She's going on maternity leave starting next week.
Literal
She [topic-は] next-week [from-から] maternity-leave [to-に] enters.
産休に入る (さんきゅうにはいる, 'to go on maternity leave') is a set phrase — 産休 is a common abbreviation of 産前産後休暇. から marks the starting point. 入る ('to enter') is the standard verb for beginning a period of leave.