。
She was afraid of the dog.
Literal
She [topic-は] that dog [object-を] feared.
恐れる takes a を-marked direct object — 'to fear X' — where English uses 'be afraid *of* X'. In casual conversation about a frightening dog a native speaker would more likely say 怖がった or その犬が怖かった; 恐れる carries weightier connotations than 怖がる, leaning literary or consequential. You 恐れる failure, judgment, or the gods more readily than you 恐れる an animal. Reaching for 恐れる here is grammatically clean but feels textbook-formal — useful for showing how the verb attaches to its object, less useful as a model of natural speech.