Gobae: I see, that clears up my questions. That is kind of a hard situation because you can't really set up signs ahead of time with the interpreter, nor is there any reason to since they won't be recurring. (For some reason I was under the impression that you were the teacher.)
Hmm, you're right, this can be touchy. Clearly the interpreter was not well educated in technical jargon, but she probably wasn't required to be for a class called "Implications of Deafness" so I don't blame her. I'm trying to put myself into her shoes and think what you could have done to avoid offending anyone.
You could say in advance "I need to ask the teacher something. Are you familiar with terms like..." and then give a few example. If she isn't and she has a good ethical background, she will admit that she isn't, at which point you could suggest that you and the teacher simply write back and forth and she could join you in case of communication difficulties that she CAN help with.
I suppose it depends on the interpreter but this wouldn't offend me. I would much rather have the clients communicating together in a case like this, as long as both of them are okay with it! However, some people could take this personally, I guess. It's the chance you take but realize that a good interpreter knows her limits and is willing to be flexible in cases like these. It doesn't do anyone any good if the interpreter is HINDERING communication and she should know that.
If you don't have the opportunity to set it up in advance -- for example, you find yourself in a situation like you describe where it starts to dawn on you that the interpreter isn't helping, I would simply say, to both interpreter and teacher, something like "Do you mind if we write back and forth? This technical jargon is a little confusing." Again, a good interpreter will not take offense at this.
Does this help answer your question?