。
She lost herself in drink.
Literal
She [topic-は] drinking-alcohol [in-に] indulged.
ふける ('to indulge / immerse oneself in') is a strong verb of absorption, taking its object with に — ~にふける. It pairs with vices, hobbies, or contemplative activities equally readily: 読書にふける ('lose oneself in reading'), 思索にふける ('be lost in thought'). When paired with 飲酒 ('drinking alcohol'), it carries a clear flavor of dissipation or escape — 'gave herself over to drinking.' 飲酒 is a Sino-Japanese compound (飲 + 酒) common in formal contexts (飲酒運転, 'drunk driving') but rarer in casual speech, where 酒を飲む is the everyday phrasing. The combination of 飲酒 + ふける lands the sentence firmly in literary or journalistic register.