Everything is simple. Quinn is an ordinary tsundere who shows her feelings and emotions to the boy through aggression, and not through affection and attention. Her behavior is no different from the behavior of a school bully in love.The special treatment doesn't appear at the start of the game, and it didn't appear overnight, it accumulated over the course of the whole game.
If you would have been more attentive, you would have noticed that Quinn requires multiple checks throughout the game:
One of the most important ones for her feelings towards the MC is the event in Episode 6 when MC could or could not help her out, which is quite heavily constrained by other factors (DIK Affinity, non-involvement with J+M, and having smoked with her on the rooftop), so it's impossible to get it if you don't have the right factors lined up.
Moreover, if you don't get this particular option in 6 or if you don't use it, it's detrimental to any sort of future progression of the MC with Quinn. Their interactions become much more limited and not as intimate as they potentially could be in the future. This is vastly different from the Mel + Sarah scene in 5 which is just a nice sex scene you could get if you have a Massive DIK status. Their sex scenes and interactions, later on, don't depend on if you had any interactions with them before, and you could get them independently from each other.
So, in a nutshell:
Make the choices that will get Quinn to like you --> Spend some time with her when it's possible thus have her like you even more --> Reap the benefits of said special treatmentIt's not that hard
P.S. No one's saying that she's a virgin, 90% of the game's female characters aren't, but your arguments are deeply flawed and could be refuted easily if you actually play the game to see it for yourself
The most important consequence for Quinn after episode 8 is that all the characters already know that she likes MС. I don't know if they will somehow make fun of her or MС about it, but I would like to see.
