。
She had to accept her fate.
Literal
She [topic-は] her own fate [object-を] accept [must-なければならなかった].
受け入れる (受ける + 入れる, 'to receive + to put in') is a compound verb meaning 'to accept, to take in.' Distinct from 受ける alone, which is a more neutral 'receive' — 受け入れる adds the sense of internalizing or making space for the thing received. ~なければならない is the obligation pattern; past ~なければならなかった makes it a past obligation. The pairing has the gravity typical of resignation to circumstances beyond one's control.