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She sings better than any other girl in the class.
Literal
She [topic-は] class [of-の] any girl [than-よりも] singing [subject-が] is-good.
Another variation on the comparison-by-universal frame: どの女の子よりも ('more than any girl'). The どの~よりも template is the productive way to express 'more than any X' — どの本よりも (more than any book), どの先生よりも (more than any teacher). Notice how Japanese builds these absolute superlatives compositionally: a wh-determiner (どの) singling out 'any of them,' a noun specifying the comparison set, the comparative よりも tying it to the predicate. 上手 here is the formal-leaning standard form for 'skilled,' contrasting with the more colloquial うまい which sounds more impressed and less measured.