You know, I was wondering about that myself some time ago. Especially after we saw real Grace that one time in front of dragoon and then in the cage again. And what comes to my mind is... lazy writing of a character.
Grace has been left alone for small amount of time before going into academy. Her family was there for her entire life before that and giving their personalities there was no way she would have been anything other than empathic and kind. The little explanation we got was that one segment from her flashback where she says "nobody is here with me now so I must give it my best". And her best was to shout on servants and act as a bully?
Look at this:
This is a face of a girl who didn't saw her grandmother for quite some time (I am pretty sure it is Grace's reaction as Ken didn't even know before this that grandmother exists) and you are telling me that this is the same person that would bully people around and push them from the stairs?
Poor original Grace was written to be a villainess for the sake of needing one for the game. She didn't deserved that fate at all, damn those lazy writers at game studio... Good thing for Ken to be isekai-ed into her and fixing the entire thing.
