Nikolas didn't stop Helena from doing anything to Robin.
When did Helena ever care about tolerance to Robin?
When she could use it to show Nikolas that she was better than Stefan, who didn't want Nikolas near the mob-friendly HIV positive daughter of Robert Scorpio.
So no, Helena never cared enough to make Robin pay for anything. She was much more interested in using her to score points against Stefan with Nikolas.
Helena hates any woman near Nik.
That actually was discussed repeatedly when Helena came to town after Nikolas was shot.
Which has nothing to do with Robin being on Helena's hit list. She was a female near Nik. Nothing more.
