Canadian Chica: Kinda my take on the Doctor's future companion
Child of the TARDIS
She, like her driver, was the last of her kind. A type-40 TARDIS, with a broken chameleon circuit that was stuck on a 1950's police box, who had faithfully traveled across the universe, backwards and forwards in time, and even over dimensions. She had sat quietly and felt her insides shift time and time again, to better suit her driver's present form and her own boredom. With her driver, she had been the home of Time Lords, humans from across the eras, robot dogs, and a transport for a host of other beings for over eight hundred years. As with most things that reach maturity though, and even if they were the last of their kind, she now had the irresistible biological urge to breed.
This was not easy as her driver had no sense of this, and couldn't even help her if he did. The Time Lords who cultivated her kind were long since dead, but they would have merely sped up this arduous process. She had no other of her kind to share her biological code with, and even if she did she would need assistance to share it. Her driver thought that she would die the last of her kind, and he along with her; oh how little did he know.
Over the eight hundred years of travel, the ol' girl had picked up a few things that did help, and now were finally coming to fruition. Regeneration after regeneration within her had always left behind residual energy; energy which she happily absorbed for her driver and companion's safety. She kept that energy close to her heart, feeling comforted by the presence of something wonderful and never knowing how essential it would be to her species' survival.
It was nearly one hundred and fifty years ago that she essentially 'acquired' the next piece she would need. Her driver had been forced to stare into the eye of harmony, and with him his beloved enemy tried to draw from it. She took from her driver what had made him human, and took from his enemy hatred and cruelty when he had fallen into it. These mixed with the regeneration energy she had stored, just another acquisition she kept close to her heart; you never knew when such things may come in handy.
Not even half a century after that everything was put into jeopardy. Her driver had been forced to use that horrid 'moment' to destroy his kind, her kind, and a most hated and feared enemy. More regeneration energy for her to store, despite her weakened state, and suddenly she only had her driver to communicate with. Her kind was gone, and silence nearly overwhelmed her. Such power from such a weapon mixed with energy and humanity and cruelty to make something different than just pieces she was storing.
It was when Rose Tyler, a golden child who helped saved her driver from the silence, looked into her heart, that she was finally able to turn that 'something different' into something real. While Rose Tyler took the time vortex into herself, she took a piece of Rose Tyler into her heart as well. That single piece gave the 'something different' a blue print to follow, and soon the 'something different' became the first stirrings of her unborn child. A child she kept sequestered deep in her heart, nurturing it in the Time Vortex and singing to it softly the song of the universe.
When she died being pulled across the void, she feared so much for her child. She was sure that her death also meant the end of her child, without anything to keep her child alive she felt the loss strongly in her last moments. A gift of ten years though, brought her back to life slowly, and assured her that her child was not lost. Her child was stronger than that; her child could even survive the bastardising of the last TARDIS into a paradox manipulator.
Having doctor-Donna connect with her was the last piece her child needed to finish its shaping. Humanity from her driver, a piece of a heart of a human girl who loved her driver, and the mind of a human with Time Lord physiology, shaped her child into the shape of a growing human girl. With more one burst of powerful regeneration energy, her daughter began to grow in earnest.
It would take years for her daughter to grow. It would be years, decades, centuries, even millennia maybe for her daughter to be strong enough to live outside her mother's heart. So she sang to her daughter, filled her head with all the knowledge she could spare; stories of lost worlds, including the beloved Galifrey, and of worlds just being born into the universe. She sang of the doctor's companions; of the beloved Sarah-Jane, Rose and Donna who kept giving so much for her driver. She sang to her daughter of passion and love, in hopes that it might decrease the hate and cruelty that her driver's beloved enemy passed on. She sang so long to her daughter, that she hoped it would be forever apart of her, even in her name.
Canadian chica: There, now it's out of my head. My belief on the origins of River Song, so I had to get it out there before it's revealed. Apparently it might be this upcoming season. Cheers!