Well I just zoomed through from the start of the Prep party where you meet Riona all the way to that moment Quinn and even though I gave Riona all 5 of my $, it didnt change anything. Quinn still rejects the MC's help. In my main playthrough, my MC in Neutral affinity, took Quinn's number, "bought" Riona and Camila, won the cum-petition, and smoked with Quinn on the roof, even had a couple of good Rooster interactions and the good text chain in Ep 5.
So not sure how you were able to get that on the CHICK route because according to the walkthrough by
rick87, you can only get that if you're on the DIK path, not on M&J path, used Quinn's services, and had sex with her in Ep 4. Perhaps the official walkthrough will clear this up in a couple of weeks, but for now it looks you got lucky somehow.
The thing for me is that, narratively, I don't think it makes a whole lot of sense depending on what your relationship with Quinn is like. The only things I haven't done on my main save are have the threesome and stay with Sage which would give me that scene with her in her room, but that's it. The MC still took her number, used her services, fucked her during the cum-petition, and had sex with her in Ep 4, and even though he didn't stay with Quinn and find out that Quinn talks about him a lot which might indicate that she likes the MC, that is still true whether he hears about it or not.
So, narratively speaking, I don't see what the MC has really done differently that would make Quinn not want his help. I could do a DIK run making the same choices with Quinn but just have DIK affinity, and she'd accept. It feels like another one of those cases where affinity is needlessly hampering the content players receive in order to force replayability even though, from a character relationship standpoint, there can be nothing that really separates a DIK and CHICK MC making the same decisions with regards to Quinn interactions apart from this arbitrary metric.