@Pipi She isnt being stubborn, shes asking to be treated like her opinion on anything actually matters. Literally just filling her in on information isnt an egregious task, she isnt even asking to be directly involved in the movements against the duchy, but he refuses to give her even the bare minimum in that regard with no concern to how being shut out and shut down affects her.
Whether Riftan wants to admit it or not, this does involve her and she wants to be included, even just on an information level. Pushing her out isnt going to do anything but stunt her growth and make her feel worse.
