。
She takes a cooking class once a week.
Literal
She [topic-は] week [per-に] once cooking [of-の] class [object-を] takes.
週に一度 (once a week) is a standard frequency expression: [time period] + に + [frequency]. 料理の講習 (cooking class) pairs 料理 (cooking) with 講習 (short course/workshop) — more formal than the casual 料理教室 (cooking classroom). 受ける (to receive/take) is the standard verb for attending lessons or classes.