。
She told me a secret.
Literal
She [topic-は] me [to-に] secret [object-を] taught.
秘密を教える ('tell a secret,' literally 'teach a secret') is the standard collocation. Note that 教える in Japanese is broader than English 'teach' — it covers teaching, telling, informing, letting someone know. Using 教える for a secret rather than 言う ('say') frames it as imparting privileged information — telling someone something they couldn't have known otherwise. Compact sentence with a useful pattern: subject + 私に + Y を + 教える for any kind of telling-a-piece-of-information.