I'm guessing the following of her background.
1. She is the second daughter, no the second child, that means that she probably has san older half sister and brother.
2. Her mother didn't abuse her, it was the siblings, that's why she has a good relationship with her.
3. The mother is the new queen, probably the mother of the other children died, that's why everyone were helping them to bully her. Because she was not the original queen.
4. There are come mangas where all the children have rights to inheritance and it's up to the father to choose the successor, maybe as he loved this new wife more, the children thought that he'll make her daughter the following ruler