So like she is an yandere for the MC, sees the retard teacher as an huge red flag/problem and has no issues with "cleaning him up" if you will. Sees the sister as a potential love rival and thus kinda plays with her/fucks with MC plans to steer shit up or to understand the situation better?
With sister at 99% understanding this could either end soon, or get made longer by her dropping the % like she already did once I think cause of the retard teacher. Question is will she at 100% become a sister and no wincest stuff happening so that yandere and MC love story will become the main topic, or will there be another "learning" this time romantic towards MC progress and battles with yandere will ensue.