She was born to the Queen of the Water kingdom a duke that her mother favoured. Though her twin was the child of the king, the people were unaware of this and so the King believed that both of them were the children of the affair. Furious, he decided the only way to calm himself was to hide the twins away as he knew they'd cause a huge scandal that he couldn't afford. The mother agreed to this except that they were allowed to return to the palace for the summer as nothing but friends to their older siblings.
The two were sent to live with their aunt and uncle who resided in Earth. Their aunt was a soldier and spent most of her time in war but their uncle was their hero. He was loving and affectionate and treated the two girls as his own. They didn't have their own children due to their uncle's infertility nor did they adopt since their aunt was gone for so long each year.
For the first twelve years, they had a happy life. They attended school and had friends, only slightly understanding who they were and their parentage meant. Charlie was happy it was just her sister and her uncle in her life, as well as her friends at school. She didn't like her aunt, thought she was cold and harsh and often threw tantrums whenever she was home.
When she was twelve, her uncle began to develop dementia. For three years, Charlie and Christina hid it and their aunt went along with it since it didn't particularly bother her career. But when she was fifteen, her uncle tried to kill them. He'd eventually gotten so bad that he forgot who the twins were and thought they were trying to kill so he defended himself. By using his powers, he tried to drown them then stab them with kitchen knives. They were saved by a neighbor who heard the commotion.
With the dementia revealed, their parents stepped in and institutionalized their uncle and their aunt was pulled out of the war. The parents and aunt settled on shipping them to the academy as the only reason they didn't drown is because of their own power and that Christina revealed powers only a princess could have. Not wanting this, Christina convinced Charlie to leave and run away with her much to Charlie's hesitance but with the threat of being separated from her twin, she agreed to do it.
For two years, they stayed in one city to the next, doing online schooling and avoiding elemental's, knowing that the officials knew that Christina was a princess and would want her back. When they were seventeen they were eventually caught and taken to the academy.