Anin is very angry at Pin for accepting to marry Kuea and I understand her BUT I'm afraid I'm siding with Pin on this one.
Because, besides what it would to her reputation, to her family's name, the fact that they don't belong to the same social class, that she's following her duty, that she's being loyal to her aunt, and all the reasons that motivate Pin to take this decision, the thing that in my opinion really determined her, is Anin saying she'd give up her title.
Because giving up her title is giving up her family. And Anin, with all the love she has for Pin and her family as well, is still a bit self-centered, and selfish, and probably not as mature as Pin because it had never been asked of her to be. So, when in the middle of her righteous fight for her love she throws that she's fine with being disowned, abandonning everything and eloping to another country, Pin has to stop it. She can't bear it. Because SHE knows what it is to lose your family. She lost her parents as a child, and all she has left is her aunt who, despites her genuine love for Pin, is not always the gentle parental figure someone like Pin might have needed. She can't watch Anin throw away something so important for her. She could not stand to be the reason the love of her life lost her family, and felt the same pain that she did. Because unlike Anin, she knows what it means to be all alone in the world.
So she had to put an end to this and say she'd marry Kuea. To protect Anin from the pain of losing her family, because she knows how much she loves them and how much they love her
