What part of the story made you think that Rinny planned all along to leave her friend in prison forever? Does that mean you've interpreted the story as Rinny deceiving you and just stringing you along from the beginning? If so, what happened in the game to make you come to this conclusion?
I actually do need to take this seriously, because I feel like I wrote the story to allow the player to understand why Rinny did what she did and be sympathetic towards her. So for that to completely not land for you (and others) means that either it was too vague, or I've messed up somewhere.
I'm not saying your experience is wrong of course. Everyone is meant to interpret the story as they will. This is more for me to improve my storytelling skills.