、。
She hates fish and never eats it.
Literal
She [topic-は] fish [subject-が] strongly-disliked is, [and-で] never not-eat.
Two patterns combine here. 大嫌い prefixes 嫌い ('disliked') with 大 ('big') as an intensifier — the equivalent escalation chain runs 好き → 大好き ('love') and 嫌い → 大嫌い ('hate'). The が on 魚 is the standard particle for the 'object' of emotional adjectives like 嫌い, 好き, 怖い, 上手, where Japanese treats the thing felt about as the grammatical subject of the feeling. The te-form ~で connects the two clauses ('she's a fish-hater, and...'), and 決して~ない is the tight pair for absolute negation: 決して on its own implies a strong negative is coming, almost obligatorily.