I've met such (male) frontend developers before, totally clueless when it comes to the DOM and how it works. Not putting any judgment in that really, tbh, because the React development model is superior for anything non-trivial (like a signin form).

In this case though, I believe she isn't confused as to how to call the APIs, maybe not even as to how to handle the response with JS and update the DOM. I think the question sounded more like you're not allowed to use Javascript at all.