。
She practices English conversation by listening to the radio.
Literal
[topic-は] radio [object-を] listen-and English-conversation [genitive-の] practice [object-を] is-doing.
Two te-form / ~ている constructions chain back to back: 聞いて ('listen and') links into the main verb 練習をしている ('is doing practice'). Note 練習をする ('to do practice') uses the separable form with を, distinct from the fused 練習する — the separable form makes it easier to attach modifiers to the noun. NHK's English-conversation radio programs have long been a fixture of Japanese self-study, some running for decades and outliving generations of learners.