。
Where on earth did she go?
Literal
She [topic-は] where [toward-へ] went-ended-up [question-の].
行っちゃった is the casual contraction of 行ってしまった — てしまう regularly contracts to ちゃう in speech, making for a snappier, more conversational feel. The tone is closer to spoken life than its uncontracted twin would suggest, slightly impatient or exasperated about the whereabouts.