。
She's good at typing.
Literal
She [topic-は] typing [subject-が] skillful.
The classic skill-predicate frame: [subject]+は+[skill area]+が+[skill adjective]. Predicates of skill, ability, and aptitude (上手, 下手, 得意, 苦手, うまい, 流暢) take が rather than を to mark what they're about — this is a different syntactic family from transitive verbs. So you say タイプがうまい, not タイプをうまい. Each variation in the skill word shifts register: タイプが上手 (neutral polite), タイプがうまい (casual warm), タイプが得意 (suggesting it's one's strong suit), タイプが下手 (the negative).