I really wish the prince had actually told her the big contrast between the two girls, rather than internalizing that analysis. If he had, it might have made things clearer for her.
@mahtan I interpret it as both girls being the type of "gamer" that uses a walkthrough to get their desired results, rather than trying things on their own, and if it doesn't work, going back and trying something else. My guess is that games like this, with multiple paths, would encourage the use of walkthroughs to try to "complete" the game as quickly as possible with all routes successfully completed, including unlocking any hidden routes. After all, if there are 5+ routes, and each one takes many hours of gameplay, you are looking at a lot of time spent, even if you do everything perfectly the first time for each route. So she is following the "walkthrough" and even though things don't seem quite right, she doesn't know how to correct it, because she never "played" the game on her own in the first place.
The idea that games like this have a lot of players that use walkthroughs and don't know how to adapt if the walkthrough is wrong also would help explain why so many in this genre have plots where when things start going differently, the "heroines" don't know how to respond, as well as the MC not knowing what to do when they don't know the future anymore, because they were basing their actions on what they knew of the game.