。
She is a taxi driver.
Literal
She [topic-は] taxi [genitive-の] driver is.
である is the formal/written copula, used in essays, news writing, biographical entries, and other expository prose — it gives the sentence a stiff, factual, almost dictionary-entry feel. The triplet だ (casual) → です (polite) → である (formal/written) is an essential calibration tool for register, and slipping between them changes how the same content lands: conversational fact, polite fact, or stated-for-the-record fact. タクシーの運転手 stacks two nouns with の to mean 'taxi driver' (literally 'driver of a taxi'); 運転手 is gender-neutral.