I thought Mary either in thoughts or talking to Addie had already told the audience that Alicia was a princess hidden in an orphanage way back, or is the trope that common I'm mixing it up with another of these villainess farce stories?
@piay123@JWChibi past chapter said that her face looks like the queen (especially her eyes), so maybe she is from a direct line meanwhile Patrick from a branch family.
Patrick is not a prince, he is the heir of a ducal house and a future Duke. Alicia is the long lost princess of their country as Mary told Addie back when Alicia first appeared.
The premise of the manga is that Mary is an isekai'd girl who knows the game inside and out. The only person she ever tells the future course of events to is Addie. From other people's perspectives, her actions just happened to have certain consequences. Without knowledge that she is guiding things in a certain direction, they wouldn't question why her actions are triggering those effects.