。
She hit the ball hard.
Literal
She [topic-は] ball [object-を] strongly hit.
強く is the adverbial form of 強い ('strong') — the い-adjective shifts to く to function adverbially. 打つ ('hit, strike') is the general-purpose verb for striking — used for hitting balls, typing, ringing bells, even shooting (打つ has the homonymous 撃つ for shooting). Without further context, this could be baseball, tennis, or any ball sport. ボール itself is a katakana loanword from English 'ball.'