。
I wonder if she'll dare go into that forest.
Literal
She [topic-は] daring that forest [into-に] enter-going [I wonder-だろうか].
~だろうか (or polite ~でしょうか) marks a self-directed wondering question — 'I wonder if X' — softer than the bare ~か question form. 思い切って (the te-form of the compound 思い切る, literally 'cut off thoughts') carries a 'daring to / mustering courage' nuance, rendering the entry into the forest as a courageous or reckless act. 入って行く is a manner-of-motion compound: 入る ('to enter') + 行く ('to go') = 'go in / venture in,' with the directional 行く emphasizing motion away from the speaker's vantage point.