。。
Was she a high school student? Yes, she was.
Literal
She [topic-は] high-school-student was [question-か]? Yes, that-is-right.
Two sentences fused into one entry: a polite past question and its affirmative answer. でしたか pairs the past polite copula でした with the question particle か — a textbook construction. はい、そうです ('yes, that's right') is the stock affirmative response when confirming an attribute or category. Note the past tense in でしたか asks about a past state ('was she'), not the present — Japanese tense tracks the time of the predicate's truth. 高校生 specifies the senior-high level (typically 15–18); contrast with 中学生 (middle school) or 小学生 (elementary).