It can be very tiring to speak in your non native language so it isn’t surprising that when in the presence of other speakers of your native tongue you might lapse into your comfort zone. If OP’s daughter wasn’t there when the conversation started it’s not too surprising that they started in their native tongue. Obviously, in an academic group setting like this, the proper response would be to switch to English when another student who could benefit from the conversation arrived.
OP’s daughter could say something like, “Excuse me, are you discussing problem X? I was really wondering about that too.” That should shock the TA into awareness of situation and cause the conversation to go to English without her having to specifically request English. It’s kind of a face saving thing for everyone.
If she is ignored or rebuffed than she needs talk to the professor.