I think she is overthinking it. Students and TA were, probably, just carried away by the conversation. I think most foreigners are less sensitive to tolerance / intolerance than Americans (in a good sense of it).
I would say to TA, “Sorry to interrupt, I see that you have a great conversation here. May I participate? If not, could I schedule another time with you for my office hours?” I don’t understand how such request may offend anyone. I, personally, would not go to complain to the department head. Unless she really wants to complain.