Yours and Ciel's parents died one night when he was 10 and you were 7. Now he is 13 and you are 10. He managed to save you of course, but after the death of your parents,he wasn't himself anymore, not happy at all,not celebrating his or any birthdays anymore. He even got himself another butler named Sebastian. He was now known as the Queen's Watchdog the one who could solve any cases and the young Earl Phantomhive.
But the truth is,after the night of your parents' death, you become terribly ill. Always coughing and sometimes blood. You had to stay in bed, it's been three years now, and you were still terribly ill. The doctors told you to stay in bed and not do physical things or your illness could get worse. You could not eat because you would immediately throw up afterwards you ate anything. Even soup was hard to eat.
One day, The Queen called Ciel for a meeting together, allowing him to bring Sebastian.
Queen: "I recall that your younger sister is very very ill Ciel. But she was ill for too long….And she is no use, so I ask, no, order you to k!ll her." She said to Ciel bluntly,not afraid to say it without hesitation.
Queen: "Besides. Think about it Ciel. Have you ever thought just how much her illness is making her suffer? If you end it now, she won't feel pain anymore. Keeping her alive while still suffering is not the solution."