Hi jk,
Great question about this Strengthening Principle question.
And this is a skill that lawyers have to apply all the time when dealing with a law's application and when the wording of a law might be open to interpretation. It's very likely that as lawyers we will all have to, at one point or another, argue for an extension of a law to what is arguably ambiguous circumstances. That's what's happening here. Note that in the principle described, there could be an argument that the department store did not "knowingly aid[] someone’s infringement" because they merely provided a open self-service kiosk to the infringer. In other words, Grandview was not the cause of the infringement, the customer was. That's what Grandview would probably like to argue, if accused of infringement. Here Answer (E) eliminates the infringing customer as the sole cause of the infringement and it justifies the inclusion of the department store as a cause for the infringement. In other words, focus on the causality that the stimulus offers always.
Also, I am not sure that "monitoring" of the kiosk is brought up either in the stimulus or the answer choice. It could be, for example, that Grandview just needs to close the kiosk entirely and thereby end its participation in the infringing activity.
Thanks for the great question and I hope this helped.