I feel bad for Quinn, the more we see of her past, the more it all makes sense.
Since she was very little, her dad has been grooming her to work in the drug business; don't trust anyone, don't let your guard down, always try to be 2 steps ahead of everyone else.
Although she seems tight with Riona, it's clear she's only trusting her out of necessity, and doesn't confide in her any more than she has to. Like her dad says:
Rox: "And even if you're forced to trust someone else... Keep them at arm's length without letting them know about it."
What kind of fucked up way to live is that?
And now her dad's gone (dead?) she has no one. Even Buddy, who seems to be running the show in Rox's absence, Quinn was told by her dad to keep "at arm's length".
Ultimately she's alone.
But with the mc it's different. She plays it tough, she tries to keep him at a distance emotionally, but he's getting to her. She wants to be close to him, she longs for it.
At first he was just another freshman for her to have fun with, screw with his mind and all that. But it didn't take long for him to start getting to her. Throughout the whole story she's been dropping her guard around him more and more, breaking her own rules, he actually makes her happy.
All the times Quinn let her guard down around the mc (not including episode 9).
And I don't think she's playing the long con, using him for some patsy for some scheme she's got going on - in episode 7, when he falls asleep on her bed, she cuddles up to him, just for a while. She longs for that intimacy she has been denied by her dad's teaching.
So yeah, her narcissism stems from her perpetual self preservation instilled in her from her dad, but a psychopath? I don't think so. Most of her unpleasant behaviour seems to be a cover, hiding her own vulnerability. But hopefully she'll learn, even if there is an inherent risk in letting people into your life, it makes life all the much better to live.
Of course, none of this is an excuse for her behaviour, just the reason for it. In real life, this is not the kind of woman to get involved with, you'll inevitably end up going down with her, or because of her. But it's porn game, and she's fun.