。
The apple was cut in half with a knife by her.
Literal
Apple [topic-は] she [by-によって] knife [with-で] half [in-に] was-cut.
によって is the formal passive-agent marker, common in written/news Japanese. 半分に切る ('cut in half') uses に to mark the resulting state — the same に-of-result that pairs with verbs like なる, する, and 切る for transformative readings. The whole sentence is a textbook example of passive transformation — quite stilted in natural use.