。
She got lost in the forest.
Literal
She [topic-は] forest [in-で] road [to-に] lost ended-up.
道に迷う (みちにまよう) is the set phrase for getting lost — literally 'to be confused about the road.' The ~てしまった adds a sense of regret or unfortunate completion: she didn't just get lost, she ended up lost, with the implication that it was unintended and unwelcome. This is one of ~てしまう's most common functions — marking outcomes the speaker wishes hadn't happened.