。
She pretended she didn't know anything about it.
Literal
She [topic-は] that matter [about-について] anything [also-も] not-know like-ような pretense [object-を] did.
~ふりをする ('to pretend') is the standard idiom for putting on an act — the noun ふり (from 振る 'wave / act in a particular way') captures the performed appearance. Combined with ~ような ('like, as if'), the construction frames the pretense as 'an act of being in a state where she knows nothing'. The 何も + negative pattern blanket-denies any knowledge. Japanese covers 'pretend X' efficiently with a structure foreign to English, which separates 'pretend' as a verb and 'know' as its complement. Note also について — the cleaner of the about-particles, fitting both casual and formal registers.