How many female superheroes are in Marvel Comics?
female refers to gender = 'Female'; Marvel Comics refers to publisher_name = 'Marvel Comics';
SELECT COUNT(T1.id) FROM superhero AS T1 INNER JOIN publisher AS T2 ON T1.publisher_id = T2.id INNER JOIN gender AS T3 ON T1.gender_id = T3.id WHERE T2.publisher_name = 'Marvel Comics' AND T3.gender = 'Female'