My friends go into the exam room with me all the time...not to interpret mind you. But just as support or whatever. I have never been told they shouldn't - by anyone. Both my parents are medical professionals too.
No real interpreter, means I write back and forth. SOMETIMES I will have a friend or support person repeat, verbatim, what the doctor said to me because I can read their lips far better than the doctor with a strong accent and beard or something but it verbatim outloud oral "interpreting" that the doctor monitors as it goes. Because of that it seems far more acceptable.
First interpreter - a Long long time ago. Long. I can't even remember. I can remember the first when I moved to Toronto because they had a broken arm and no teamer. I remember showing up and firing them after learning it was their dominant arm that was broken and only understanding because of their obnoxious lip movement to accompany the hand flapping....