In Wuthering Heights, what do Catherne Earnshaw's incribed volumes reveal- especially about past conflicts?

Zillah quietly shows Lockwood to a chamber which, she says, Heathcliff does not like to be occupied. She doesn't know why, having only lived there for a few years. Left alone, Lockwood notices the names "Catherine Earnshaw," "Catherine Linton," and "Catherine Heathcliff" scrawled over the window ledge. He leafs through some old books stacked there, and finds that the margins are covered in handwriting––evidently the child Catherine's diary. He reads some entries which evoke a time in which Catherine and Heathcliff were playmates living together as brother and sister, and bullied by Joseph (who made them listen to sermons) and her older brother Hindley. Apparently Heathcliff was a 'vagabond' taken in by Catherine's father, raised as one of the family, but when the father died Hindley made him a servant and threatened to throw him out, to Catherine's sorrow.