Once upon a time, she was born in a time that is now the future. (For her, time is not a straight line, but a myriad of circles that overlap and intertwine thanks to the help of a blue Police Box). In a time where her parents have yet to be born and her grandparents are still school children, she is applying for jobs to take care of children. It is wonderfully wicked and yet impossible.
She herself is impossible, but finds it easier to call herself practically perfect. Both are true. She is human, with the characteristics and abilities of a time travelling alien from a distant planet. She has the abilities to live different lives, wear different faces. She rather likes the face she now wears. It's dignified.
She straightens her hat and picks up her carpetbag. The carpetbag is bottomless , thanks to a bit of technology unheard of in 1910. She uses it anyway, figuring a little bit of magic never hurt anyone. It’s about time to go and find two young children who need her specialized brand of help and magic. She stands up, lifting off of the bench.“Good luck, Mary!” A familiar voice calls. In this time, they know him as Bert the Chimney Sweep, but she will always know him as the Doctor, no matter what his face. Somehow she knows that they will have more adventures in this time, and soon. He's having quite a lot of fun doing work that would seem rather lowly; but the Doctor has always delighted in the unusual, she thinks.
She winks back at him; and uses the parrot headed umbrella she picked up at a craft fair three thousand years for now. No matter what her name, River Song has never failed to make an entrance. As Marry Poppins, she floats on the air, determined to help out a brother and sister, Jane and Michael Banks.