Well, firstly, art teachers are not exactly known for their anti-feminism. Safe money is on her just being insufferable, especially given the fact that she deliberately left out what she said/did that got that response from the teacher, lol.
Secondly, this is objectively a moronic response visually. Not only is it a dial (which implicitly supports the teacher's premise), but it is plainly obvious that there is a LOT of room on that dial between the two settings--this implicitly contradicts the apparent intention to communicate those two 'settings' as a binary proposition. Would have made much more sense to display it as a switch, a device that actually has only two binary positions.
While I agree with you on some of the above, I disagree with your choice to insult both the artist (“insufferable”) and the art (“moronic.”) It really weakens your point when you throw ad hominems into your argument. Your valid criticisms become clouded by an apparent bias, leading people to take your point less seriously.
On the other hand, it shows that every step on the dial is a step towards being complicit in their own dehumanization. The teacher’s request seems to suggest that those are separate axes, whereas OP obviously does not think so.
If the post is honest, this is an fine response. I'm always a little skeptical of ragebait posts, but I've had plenty of interactions with educators who run counter to what you would assume of their profession.