That’s affecting a lot of us, to be sure. OP’s D just has to evaluate the situation the next time she goes for office hours and finds a group talking in some other language. If it is not a one-on-one situation, then she is not being rude if she asks for them to carry on in English.
Just as an aside, both as a TA and as a professor I’ve been warned never to meet with a student in your office with the door closed. Never. I don’t know what protocol is at other institutions, however.