I dont think she turned on him and I doubt she'll betray him in the future. Since they grew up and survived together. Plus she admires him. Like in the last chapter where she asked the knight to join their side she talked about him shining and stuff like that. I am pretty sure she's trying to get information and trust from the prince so that they can use it against him. Although I could be very wrong, but I hope not.
I think that she'll betray him, because in earlier chapters she said that she didn't want to be the "support twin" and ghat she wanted to take his place, also because even sins they were young they told her that she needed to be a supportive character to the prince or something like that, and honestly i respect that (i don't want her to take the place of Rayburn but i still want her to be a strong and independent woman)
Im gonna shave my hair if she betrays him
True, but that would be so sad
i really really wish the Prince's twin sister didn't turn on him
wanna see whose side she's really on by the end :((