This story came about from a "Complete The Story" book I picked up from Barnes and Noble. I highly recommend it for writing exercises. The prompt was just too perfect to pass up as a person whom is into Doctor Who. :) The sentences in Italics are the prompt from the book. The rest is all me.
How?
The doctors had never seen anything like it. She was a perfectly healthy little girl who just happened to have two hearts. The only explanation they could offer was perhaps she was supposed to have a twin, but didn't finish developing. It's rare, the doctors had said, but not unheard of.
Clara knew different. This wasn't a case of her pupil absorbing a would-be sibling: This was a case of a certain Gallifreyan Time Traveler's long lost daughter being found.
Jenny. He's only spoken of her, once...and even then, it was almost too difficult for him to discuss her. She'd died, he'd said. Like so many in his life. It had only been a few minutes of conversation. What she'd gathered was the daughter was a young woman...not a Third Year. Hadn't he said she wasn't enough like him? Hadn't he said she wasn't able to regenerate? Yet, that's the only conclusion Clara can reach. A young, experimental Gallifreyan, no experience, or guidance. A regeneration gone askew, landing a young woman as a little girl.
Clara smiled as the doctors released them, and withdrew her mobile. She'd practically heard his body freeze, could picture those glacier blue eyes widening as the weight of her words were considered. She didn't have to ask what he was doing at the sound of flipping levers, TARDIS locked on her phone. The blue box materialized moments later.
Fin
Author's Note: There you have it! Sorry it's so short. The book prompts are only one page long. I hope you enjoyed. Please feel free to give me constructive criticism, which, like that book, will help me improve my writing skills. Be blessed!