I would say any film can be called feminist that has female characters who have agency in their life, that are in charge of their fate or do important things or take up half the space. I would consider a film feminist, I don't care what it's about, but if the cast was gender balanced, where it would be just as likely that the boss or the best friend or whoever was female. It's really as simple as showing women being in charge of their destiny and giving female characters a voice.
