。
She pretended to be a student.
Literal
She [topic-は] student [attributive-の] pretense [object-を] did.
~のふりをする ('pretend to be / act as if') is the standard Japanese pattern for putting on an act. ふり ('air, pretense, manner') is a noun derived from 振る ('to wave / shake') in its extended sense of 'behavior'; pairing it with する gives 'do the pretense [of being X].' The の links the noun (学生) to ふり attributively. Note the contrast with ~ようなふりをする (a more elaborated 'pretend in a way that resembles X') and ~ごっこ (children's pretend-play, like お店ごっこ 'playing shop'): each captures a different flavor of pretense. 学生のふりをする could be motivated by anything from getting a student discount to deeper deception.