。
She's terribly afraid of the dark.
Literal
She [topic-は] darkness [object-を] greatly is-fearing.
Note the particle pair: 暗やみをひどく恐れる takes を on 暗やみ rather than the が of emotion-adjective frames (彼女は暗やみが怖い). The verb 恐れる ('to fear') is transitive — it takes a direct object — unlike the adjective 怖い, which makes the cause of fear into a subject. 恐れる leans more formal/written than 怖がる. ひどく ('terribly, severely') is the adverbial form of ひどい. 暗やみ is just a hiragana spelling of 暗闇.