I'll just put it out there. In a hierarchical society, to mess with someone like the Duke's fiancee you either have to have a superior backing or be an idiot. Especially if said fiance was approved by the big boss man himself (king/emperor). It rarely happens in these novels/manga/manwhas that someone uses their power/status to squash the bullies. After all, it is more satisfying if the MC does it herself without help. Just that sometimes I want to ask the bullies, you do know who you are poking right? If something goes wrong it can easily turn into an "off with her head" or poisoned last meal in prison kind of situation.
On another note: the duke seems to be sending her gifts because he thinks that is how a wife should be treated. Kinda awkward. They need to talk more. Connect more. Fluffy times more. Kyaa!!! DokiDoki!!!! more. 😀 All for my enjoyment.