Like any historical artifact, this song can be difficult to judge from outside of it's own time and context. The things that made Missy Elliot revolutionary at the time of her peak popularity don't stand out now because they've become commonplace. When Elliot first debuted she was a larger black woman (years before Lizzo!) who was noted for being ashamed neither of her size, nor her color. That was groundbreaking at the time. She also wasn't trading on her sexuality, at a time when many of the top female names in popular music were sex kittens who played up their desirability to men as their primary attraction. She was an unabashed eccentric (years before Lady Gaga!) at a time of conformity --initially infamous for her habit of wearing trashbag costumes on stage. There was literally nothing and nobody like her in popular culture at the time.
When "Work It" came out, it represented in some ways a new Missy. She had lost a lot of weight, and here, in this song, she was talking frankly about sex for the first time. But it was also clear that she hadn't lost any of herself along the way. The sexuality in the song is from a place of confidence --it isn't really seeking male approval. There's a level of balance, where she's expecting the boys to be as much sex objects for her as the other way around. And the funky, off-kilter visuals of the video show that she wasn't reining in on any of her eccentricities in pursuit of popularity. If anything, she was flaunting them ever more freely.
Today, with self-confident, idiosyncratic, black female figures like Beyonce, Janelle Monae and Lizzo ruling the airwaves, it's harder to see anything out of the ordinary in "Work It!" But at the time, Missy's confident self-expression and unwillingness to compromise was a breath of fresh air that was tremendously empowering to many women. It's likely this, more than any specific messaging in the lyrics or visuals, that causes your teacher to view the song as an icon of feminism.