。
She gave herself over to pleasure.
Literal
She [topic-は] pleasure [in-に] indulged.
ふける (literary 耽る) is 'to lose oneself in, to indulge in' — used with abstract nouns like thoughts, reading, memories, or as here, 快楽 ('pleasure'). The phrasing has a literary, slightly dramatic ring to it: bookish prose, biography, novels with a moralizing edge. 快楽にふける in particular tends to evoke pleasure-seeking with a hint of judgment, the Japanese flavor of 'gave herself over to a life of indulgence.'