。
She attends school.
Literal
She [topic-は] school [target-に] is-attending.
通う ('attend regularly, commute') is the verb specifically for ongoing institutional attendance — school, work, the gym, doctor's appointments, lessons. It implies repeated, scheduled visits rather than one-off going. The に marks the destination one is regularly going to. ~ている turns 通う into the steady-state habitual: she's currently in the regular pattern of attending. The polite ~ます-ています form (here ~ています) signals everyday politeness, the level you'd use in conversation with someone you don't know intimately. 通う overlaps with but differs from 行く ('go [once]') and 出かける ('go out [from home]'): each captures a different temporal granularity of going.