@CBFlap It's been established that the sister is only a half-sister, born from the Earl and Countess, not Silas's mother. The new Countess shows no respect to get step-daughter, and neither does the Earl.
As a result, the children of the two are also hostile towards her. I'm this case, the younger sister takes advantage of her mother's favoritism to get away with stealing anything she wants from her older sister.
This is the older sister merely telling the truth about past events.