Suffice to say, this was no casual friendly invitation.  This was a social declaration of war, as if they hadn’t already been waging one quietly away from the press.  If Hermione didn’t go, Jennifer would call her a snob.  If she did go, without British friends in tow, Jennifer would make a very big deal out of it since "she invited them too!"  If Hermione did go, and brought friends, well...