。
She had to go herself.
Literal
She [topic-は] [by-herself-自分で] go [must-ねばならなかった].
~ねばならない is the formal/literary obligation pattern, a slightly stiffer alternative to ~なければならない. Both built from the negative conditional + ならない ('won't do, isn't acceptable'); ~ねば uses the classical/literary negative ぬ form. Often appears in essays, news, and elevated narrative. 自分で行く ('go in person, go oneself') emphasizes that no one else could substitute. Past ~ねばならなかった makes it a past obligation now resolved.