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She's said to be the top tennis player in France.
Literal
She [topic-は] France [in-で] number-one's tennis-player is [quotative-と] is-said.
~と言われている is the standard frame for 'is said to be / it is said that' — combining the quotative と (marking the said content), the passive of 言う ('say'), and ている for the ongoing-state nuance. The agent of the saying is unspecified — characteristic of the impersonal passive, which abstracts away who exactly is doing the saying. 一番のテニス選手 uses 一番 attributively with の ('the number-one tennis player') — a standard superlative pattern.