。
She practiced her English pronunciation yesterday.
Literal
She [topic-は] yesterday English [genitive-の] pronunciation [object-を] practiced.
発音 ('pronunciation') is a tight Sino-Japanese compound: 発 ('emit, produce') + 音 ('sound') = 'producing sound.' The same 発 turns up in 出発 (departure, 'set out producing motion'), 発見 (discovery, 'producing sight'), and 発表 (announcement, 'producing display') — a productive morpheme that lets you build precise nouns from concrete pieces. 練習する is the standard verb for deliberate practice — distinct from 勉強する (studying) and 訓練する (training/drilling).