Do you mean there was more than one deaf person in the class and you guys were signing together? In a case like that I believe it's the part of the teacher to step in and say something, just as if it were hearing students talking during class and not paying attention. The thing is most teachers will ignore it because, I believe, they don't want to be seen as picking on the deaf students. I have seen teachers talk to the deaf students about it when it's been really disruptive to the class, though. Personally I find it disrespectful to the teacher when deaf students sign to each other using big gestures (as opposed to "whispering") all through the lecture, but since I work in the college setting, it's not my job to scold students.
If the student is constantly signing to ME, well, that's a different story.
However, this isn't "unwanted advocacy" because this interpreter isn't trying to help you, she's trying to punish you.