Since the teacher will not step in, I suggest that you assume an authority role when dealing with this person. Respond to her as if you’re professionally correcting an unruly third grader.
“Susie, you’ve raised the same objections many times, and it’s been explained to you why the focus of the project is not going to change. Let’s move on to something constructive.”
“Susie, that type of remark is not appropriate for class.”
“Susie, nothing is accomplished by name calling.”
“Susie, that was offensive. Please don’t use that word again.”
Do not justify or argue. Just shut her down sternly.