IndecisiveScroller

I don't think you paid enough attention. YJ was already friends with HJ and living with her and JD. She had multiple scenes where she explained her actions/decisions post-rape. It isn't that hard to understand. You don't have to agree with her reasoning but it isn't hard to understand nor was it ignored by the writers.

OP; ETA: One of the major twists is the source for a lot of negative reviews and I'm certain many either dropped it or didn't really process what was happening. You MUST suspend your disbelief and take it at face value because a) story-wise, everything gets addressed by the end and b) it is applicable to real life and your disbelief IS EXACTLY THE POINT! Your reaction is needed to finally shatter the resistance to acknowledging the depths and complexity of human depravity in order for the world to change for the better. This writing choice is actually very purposeful. And it would never hit the same if it played out differently.