Born into the upper echelons of magical society, Katelynn Grace knew from an early age that her father saw her more as an experiment than a human. He adored her, of course, just as any parent does for their offspring, but being the mad scientist that he is and having been denied all the human trials by the Ministry that he so desperately needed, who else better to use than someone close to home? His wife didn't know - there's no way she'd have let him experiment if she was aware - so from being able to toddle, Katelynn Grace was having all sorts of potions and spells tested on her. Luckily none of them were destructive (such a consequence never really came to her father's mind), and most of them didn't work at all.
With two parents in the Ministry, there was a lot of pressure on Katelynn Grace to be as intelligent and successful as them; so far, she's living up to their expectations. It was clear from an early age that Katelynn's an extremely clever child, as she was writing and adding up long before her fellow nursery kids. It also became clear that she wasn't a people person - like her mother, Katelynn has always preferred being alone. Throughout her childhood, she was perfectly happy tucking herself away with a pile of books, independently learning everything and violently refusing any help, even it would improve her progress. She's just always been like that.
The first signs of magic peeked their head rather early - when she was around six years old, and being uncharacteristically argumentative as her father tried to test a home-brewed potion on her. The bright green colour and pungent odour made her recoil and lash out, and without lifting a finger, the bottle in her father's hand shattered into pieces. He wasn't angry - actually, he was incredibly happy, and dashed to her mother to celebrate his daughter's magical abilities.
Katelynn Grace's life remained quite peaceful up until she was ten years old, approaching eleven, and her dad conjured up a new spell to test, much to Katelynn's disgust. She'd grown to hate being an experimentee, but that didn't stop her father casting a rather complex spell on her that turned out to actually work. Suddenly Katelynn found herself able to pick things up, put things down, turn things over and even smash things without moving a muscle; she couldn't control it at all, so rooms were quickly in pieces with no intention to change anything, but her father was jumping for joy. Katelynn, however, was devastated; she hated anything complicated, and suddenly being laden with this so-called "gift" terrified her.