。
She's a virtuoso typist.
Literal
She [topic-は] typing [genitive-の] master is.
達人 (たつじん, 'master, virtuoso, expert') is a richer term than the generic 上手な人 — it implies long dedication and a kind of zen-mastery feel, often used for traditional crafts (剣道の達人 'master swordsman', 茶道の達人 'tea ceremony master') and metaphorically for any deep proficiency. The kanji 達 means 'reach, attain,' and 人 means 'person' — 'one who has attained.' Calling someone a タイプの達人 is mildly playful when applied to typing, treating an everyday office skill with the gravitas of a martial art.