Responses
I belive she was testing how Violet would react to someone overstepping, and that Violets reaction aka the two slaps and statement proved to her that Violet is the person she would follow. Violet proved she had the insight to disaplin even her most beloved sister if needed, making her a vise future leader.
If she had spared her sister for the exuses it would mean Violet is open to being manipulated by those she loves, making her a failure / weak future head whom her sister would need to dispose off.
Y is she blushing???