Honestly, I'm not even worried if Vincent ever mistakes her sister as "Paula," when she's not even half of who Paula is. I think he'll end up discovering soon "Ann" is Paula. Besides, Joely is already speculative of Ann.
i'm banking on the fact that her sister is so mean that she won't be able to successfully pretend to be good. plus, we have ethan who knows MC's true face.
that was the prolly the most peaceful resolve for the inheritance