I don't think it's either of those things. As I see it MC just managed to get through Quinn "shell" which is a defensive mechanism needed in the world she grew up in. MC became some sort of confusion in her life, something that she has never experienced. And that force her to adapt, change or go through metamorphosis where Tremolo is a catalyst of this prosess. Remove him earlier from her live and that prosess won't be complete, Quinn will return to her previous self. Continue with this influence and, well, we've yet to see the result of that. And this is most definitely not an act. At the end of Quinn's hangout when she hugs MC there is no one to mislead. She even double checked if Tremolo is sleeping.
Then I wonder what the 'next move' is when Quinn is talking to Rio. Although it's only an assumption, she appears to be pointing at the MC. Unless this is camouflage...
Quinn is so entrenched in her lifestyle and behavior that I doubt there can be any seismic shift in her persona by the end of the game. But, she isn't a real person, so... The bench/broccoli scene would certainly support your theory. So would the first roof scene, the way she's looking at the MC. But, like messages here or texting, it's hard to get conversational tone, particularly the "Fuck me..." being said to an MC that's high as a kite. Plausible deniability in the making? She does like to shift blame.
To use Sage's words, the die has been cast on Quinn's personality. Even if she would clean up her act, it would take a lot of effort and probably even more time. Quinn's track record for adjusting on the fly is less than impressive.
With Rio, the seeds of doubt have been there all along. I could see Rio changing, but I'm not sure Quinn could in the short amount of time the game exists in - one American school year (that is correct, isn't it?).
I've been wrong before... I'm not looking to debate, but rather get a more granular understanding of where to things may progress.
7thOmen