、。
She pretended as though she knew absolutely nothing about it.
Literal
She [topic-は] that matter [about-について], just-like anything [also-も] not-know like-ような pretense [object-を] did.
まるで~ような is the canonical 'just like / as if' simile, with まるで ('exactly, just') intensifying the resemblance — 'as if for all the world she knew nothing'. Without まるで the sentence would still be grammatically complete; adding it pushes the comparison from neutral observation to vivid suggestion that the pretense was being laid on thick. The '、' (Japanese comma) after について signals a brief pause, separating the 'about that matter' frame from the manner clause that follows. Pretending complete ignorance is a recurring social maneuver in Japanese conversation, with its own cultural label: 知らんぷり ('feigned ignorance').