。
She was a medical student.
Literal
She [topic-は] medical-student was.
医学生 — a tight nominal compound: 医学 ('medical science') + 生 (the productive suffix '-student, one who studies'). The same 生 builds 大学生 (university student), 高校生 (high schooler), 留学生 (foreign student). Polite past でした closes the sentence, fitting biographical or introductory speech: someone is being described in a third-party context, perhaps in an obituary, alumni profile, or résumé read-aloud.