。
She gave birth to twin girls.
Literal
She [topic-は] twin [possessive-の] girls [object-を] gave-birth-to.
生む (うむ) specifically means 'to give birth to' or 'to produce.' The の links 双子 to 女の子 as a noun modifier — 'girls who are twins.' Unlike English where 'twin' can function as an adjective, Japanese uses a noun-の-noun construction to achieve the same modification.