。
She's never late to school.
Literal
She [topic-は] never school [target-に] is-not-late.
遅れる ('to be late, fall behind') takes its target with に — being late TO an event or destination. Habitual punctuality (or the lack of it) is a culturally weighted topic in Japan, where school and workplace norms expect arrival not just on time but several minutes early; 遅刻 ('tardiness') is recorded on student records and can affect job evaluations. 決して~ない ('never') applied to lateness here amounts to a small badge of pride.