。
She's very good at tennis.
Literal
She [topic-は] tennis [subject-が] very skilled.
About as bare as the skill-claim sentence pattern gets: topic-marked person, が-marked activity, intensifier とても, and the i-adjective うまい ('skilled'). Drop any of the elements and the sentence still makes sense as a fragment, which is the test of a clean syntactic core. 上手 would substitute equally well in this slot, with a slightly more formal flavor; うまい is the choice for everyday spoken Japanese.