Narcissa always had an obsession with Bellatrix. She would allow her to walk all over her, and she would love it. Simply because she would always be rewarded for her endless loyalty. She idolised the raven haired witch and had a love deeper then any should have for their sibling. This was clear during their entire upbringing. It got the two of them through some very dark times. Seeing her sister start to respect a mixed blood peasant like Hermione Granger truly did blow the blonde witches mind. She felt a sudden bout of jealousy enclose her, the fact that this outsider had her approval while she was stood in front of her sent her into a confused rage.