。
She made it clear that she disliked him.
Literal
She [topic-は] [he [subject-が] disliked [is-だ] [that-という] thing] [object-を] made-clear.
~ということ wraps a clause as a noun phrase: 'the fact that ~.' はっきりさせる is the causative of はっきりする ('be clear') — literally 'cause to be clear,' i.e., 'clarify, make plain.' A common pairing for declaring or revealing one's stance.