So, let me get this straight, not only do you want to be Quinn's "savior," you also want to bring her to the light side?

All joking aside, I've been pondering over the mechanics of this AVN. This isn't the answer you were looking for, but bear with me a minute. I too would like to know the answers to this.
Okay, so you have all of the way until flushing the papers in chapter 8 to make affinity choices. You are locked in after that one (if not before). There are at least a couple DIK choices and buying from her restaurant required to get on Quinn's path. You CANNOT date Josy and Maya. I'm pretty sure there is another LI (Jill or Bella?) that causes Quinn to kick you off her path