Ironically, CS is one of the fields that’s collaborative. Since this is a US university and an open discussion session, excluding one seems to miss that point. She has a right to listen in. Presumably, they weren’t talking about one kid’s grade. In that case, only one would be in there.
I don’t suspect this is a gender issue (or not entirely.) Maybe just something self-serving, on their part. But she’s a CS major, presumably competent to share in the idea exchange. That should be respected.