Just remember: 
Heronia is stupid, but not malicious.
Imagine a world where you knew that if you failed to follow a certain path (that is, saving the crown prince), the world would fall into certain ruin and despair. You'd be obsessed with trying to prevent that from happening, assuming you cared about the plot.
Heronia is trying to, effectively, save the world and the people around her. She's not trying to steal anyone or anything - imagine how frustrated you'd be if you were trying to save people but the world itself seemed to put events in motion that prevented you from doing so. 
Not going to deny that she's too stupid to realize that the underlying plot of the game is now totally irrelevant and that her specific route of saving them isn't necessary anymore. To her, it just looks like she's moving towards the destruction end.