。
She tapped me on the shoulder.
Literal
She [topic-は] my shoulder [object-を] hit.
肩をたたく ('to tap / pat on the shoulder') is a friendly, attention-getting, or congratulatory gesture in Japanese as in English. たたく is the broad verb covering 'hit, tap, knock, beat' — context picks the right English word. Note that the body part takes を rather than に, even though English uses 'on' — Japanese treats the body part as the direct object of the action. There's also a workplace euphemism 肩たたき (lit. 'shoulder-tapping') for a tactful suggestion that an employee retire or step down — a quiet pat that says 'it's time.'