。
She has a clear voice.
Literal
She [topic-は] clear voice [object-を] has.
澄んだ声 means 'a clear voice' — 澄む (すむ) means 'to become clear/transparent' (of water, sky, or sound), and 澄んだ is its past/attributive form. 声をしている uses する in the 'to have (a feature)' sense. This is a compliment about vocal quality — a pure, ringing clarity.