。
She plays tennis with her friends once a week.
Literal
She [topic-は] week [per-に] once friends [with-と] tennis [object-を] does.
テニスをする (to play tennis) follows the standard [sport] + をする pattern. 友人たちと (with friends) uses と to mark companions and たち for the plural. 週に一度 sets the frequency: literally 'one time per week.' The polite します at the end makes this a neutral, everyday statement — appropriate for describing someone's regular activities. テニス, like many sports in Japan, was imported during the Meiji era and remains popular as both a school 部活 sport and a leisure pursuit for adults.