Would you really specify महिला in conversation or would you just say वेटर? We even know already that the waitress is feminine from the word हमारी
You are right. We don't specify waitress by using word महिला with वेटर as the gender is already implied with the use of word हमारी . I think this translation generated by Duolingo's algorithm as meaning of waitress is given to be महिला वेटर here.
Waiter is male and waitress is female