It had taken some persuading, but Hermione was being allowed to go to the dance without Jansen or Newport by her side.  Given the use of portkeys, Hermione could have traveled with either of them, however that would have given away her identity immediately.  Instead she was allowed to change in their room, while Jansen made his way to the Great Hall.  Meanwhile, Newport would stay in the room until Hermione used the portkey, then go to the Great Hall herself.  Both of them could then circle Hermione from a distance during the party.