。
She entered that university to study English.
Literal
She [topic-は] English [object-を] study [in order to-ために] that university [in-に] entered.
大学に入る — literally 'enter into the university' — is the standard expression for 'enroll in / start attending a university.' The に marks the institution as the destination of entry, the same usage as 会社に入る ('join a company') and 部活に入る ('join a club'). The purposive ~ために on the dictionary form 勉強する frames the deliberate goal motivating the action. その ('that') points to a specific university already known in the discourse — a practical reminder that demonstratives in Japanese track conversational shared knowledge much like English ones.