。
She pretended not to know anything about it.
Literal
She [topic-は] that [about-について] anything not-know [pretense-ふりをした].
~ふりをする is the productive 'pretend to' pattern — ふり ('pose, appearance, pretense') + を + する gives the meaning 'to put on the appearance of X.' Attaches to plain-form verbs and adjectives: 知らないふりをする ('pretend not to know'), 寝ているふりをする ('pretend to be sleeping'), 嬉しそうなふりをする ('pretend to be happy'). Pair with 何も~ない ('nothing,' built from interrogative+も+negative) for the universal 'pretend not to know anything.' One of the cleanest grammatical frames a learner can master for talking about feigned states.