。
She was back to her old self.
Literal
[topic-は] again original [genitive-の] self [to-に] returned.
もとの自分 ('one's former self') uses もと ('origin, former, original') as a noun-prefix-adjective — 'the original/former self.' The に here marks the destination state of the change: 戻る ('return') with に for the state being returned to. Pattern: ~に戻る ('return to [a state]'). The また here is 'again' — emphasizing recurrence rather than newness. Without context, the implication is recovery from some change or disturbance — coming back to one's ordinary, baseline self after a difficult period. Common in stories of healing, redemption, or simply 'getting through a bad spell.'