- You may be looking for the TV story.
Sky Smith was created by Miss Myers, a member of a Fleshkind race, as a bio-weapon intended to exterminate the Metalkind. She was later adopted by Sarah Jane Smith. She was similar to Sarah Jane's son Luke in that while she had the physical appearance of a pre-teen, she was actually a "newborn".
The Fleshkind and Metalkind had been at war for centuries before "Sky" was born. Sky was created by Miss Myers (essentially her mother) as a superweapon that could destroy every single Metalkind across the entire universe. She had to be primed to detonate, which involved her being in vicinity of at least one Metalkind; she would then explode, inevitably ending her life. (TV: Sky)
Meeting Sarah Jane
Before this could happen however, she was taken to Earth by the Shopkeeper and Captain and dropped off at Sarah Jane's house where the Shopkeeper believed she would be safest. She began to blow out all of the electricity in Bannerman Road and Sarah Jane named her Sky because it seemed like she had "fallen out of it". While Sarah Jane was busy looking for where she came from, Sky was taken care of by Clyde until a member of Metalkind arrived. She found baby Sky outside her doorstep. Sky was captured by her "mother" and brought to the power plant, where the Metalkind approached her and triggered her prime transformation into a preadolescent.
Being taken from the plant, Sky was brought back to Bannerman Road, where Mr Smith told her that she was a bomb meant to destroy the Metalkind and that only Miss Myers could defuse the explosion she was genetically programmed for. As Miss Myers was bringing Metalkind to earth in an attempt to force Sarah Jane to give her up, Sky decided to fulfil her destiny and go to the Metalkind world before Miss Myers could succeed. Luckily however, Clyde Langer and Rani Chandra prevented the Metalkind from appearing and the lone Metalkind teleported himself and Miss Myers away from Earth back to the war. Due to the discharge of energy when the portal was closed, Sky's bomb status was wiped and she was brought back to Bannerman Road, where she was introduced as Sarah Jane's new daughter to the Chandras. (TV: Sky)
Part of the gang
Sky met the Shopkeeper and the Captain again in Sarah Jane's attic, where they confirmed that they were the ones who had dropped her off at Sarah Jane's. Sky wanted to stay with Sarah Jane and the Shopkeeper agreed before they teleported away. "Sky Smith" had become Sarah Jane's daughter. (TV: Sky)
Less than a month later, Sky was enrolled in Park Vale Comprehensive School. While she and Sarah Jane were being interviewed by Haresh Chandra, it began to rain fish. Due to her non-human nature, Sky was the only person who did not fall victim to the curse put on Clyde by Hetocumtek. She confronted Sarah Jane, Rani and Carla Langer and deduced that Hetocumtek was using Clyde's name to escape from his totem pole. After consulting Mr Smith for advice, she urged Sarah Jane and Rani to break the curse on themselves by saying Clyde's name and remembering what he meant to them. They found Clyde and took him back to Bannerman Road where Mr Smith teleported the totem pole into the attic. Clyde defeated Hetocumtek by shouting his name at the totem pole; the curse was lifted and the totem pole destroyed. (TV: The Curse of Clyde Langer)
As one of the top three journalists in the United Kingdom, Sarah Jane was invited to the rehearsal of the launch of the SerfBoard by Joseph Serf. She took with her both Sky and Luke, who had just come back from university. She met her old editor Lionel, and continued to amiably reject his romantic advances. Luke and Sky both noticed something was wrong with Mr Serf when he "glitched". Sarah Jane found out through Mr Smith that the real Serf had died in a skiing accident in 2007. She organised an interview with the hologram Serf but his associate John Harrison stayed with them. Sarah Jane made numerous attempts to expose Serf and finally did so as she resisted his attempt to hypnotise her. Harrison drew an alien weapon and threatened Sarah Jane. Serf was being controlled by Skullion slaves of Harrison; Luke and Sky had discovered this and took control of Serf to distract Harrison. Harrison wanted to hypnotise the entire planet via Serf so he could make billions in profit when everyone bought the SerfBoard. He then took Sarah Jane's sonic lipstick and locked her in a room with a cleaner and Luke and Sky in another.
The other prisoner with Sarah Jane was Adriana Petrescu, a cleaner who wanted to help the Skullions. They manage to escape and free Luke and Sky who had used K9's whistle to alert Clyde and Rani via Mr Smith to get the pen Harrison was using to torture the Skullions. Clyde and Rani arrived at the launch in disguise and managed to retrieve Harrison's pen. Luke and Sky took control of Serf whilst Sarah Jane and Adriana took the Skullions to the roof of the building. Mr Smith had alerted the Skullion species to send a spaceship to Earth to pick up the Skullions. Harrison took his pen back and began to kill the Skullions, but Luke and Sky used Serf to hypnotise the audience at the launch to destroy Harrison's pen, which they did. He told Clyde and Rani to go to the roof where a Skullion spaceship appeared and took the freed Skullions home. Harrison had also been beamed up by the Skullion spaceship, where Luke hoped that the Skullions would put him to work. Sarah Jane gave Adriana a card for U.N.I.T, offering to facilitate getting her a good job there. Sarah Jane and her gang then returned home. Sky was treated to a picture of herself drawn by Clyde and hung up by Luke. She then embraced her brother. (TV: The Man Who Never Was)
Sky went along with Sarah Jane, Clyde and Rani to an antiques auction. Sarah Jane bought the head of the Difference Golem Adam. They then tried to find the body of Adam at Holcote House. Since the metal body was difficult to find, Sky used her electric power to find Adam's body. After the body and head were put together, Sky activated Adam with her electric power. Later the part of Adam which contained Adam's consciousness was brought back to the future. (AUDIO: Children of Steel)
Sarah Jane and her gang continued to have adventures, defend Earth and save countless lives. (AUDIO: Children of Steel, Judgement Day) Statues were raised in their honour and they left behind a legacy that lasted forever. (PROSE: The Wedding of Sarah Jane Smith, TV: The Man Who Never Was)
Upon her transformation or "priming", Sky knew nothing of the world. In this regard, she was very similar to Sarah Jane's first adoptive child, Luke — a similarity Rani noted early on. Because of her naïveté, Sky asked many questions, wanting to know more about Earth, which she loved. Rani became Sky's guide to the world similar to how Clyde was Luke's. (TV: Sky, The Curse of Clyde Langer)
Sky enjoyed Clyde's jokes more than Sarah Jane and Rani did, and was very joyful. She could also be quite defiant and very brave. Shortly after her birth, she ignored the Bannerman Road gang's protests when she was willing to die in order to save Earth — and specifically, to save Sarah Jane, with whom she had quickly developed a bond. (TV: Sky) She later defied protests by Sarah and Rani that they didn't want to hear about Clyde again, as she was the only person immune to the curse on Clyde's name which ultimately saved Clyde and the world from Hetocumtek. (TV: The Curse of Clyde Langer)
Sky was nervous about meeting Luke in person and was initially jealous of him, but quickly she grew to love her brother as he did her. Unlike Luke, she did not call Sarah Jane "Mum". (TV: The Man Who Never Was)
Sky was created as a genocide bomb to wipe the entire Metalkind species from existence, presumably leaving everything around her unharmed to prevent her own kind being hurt in the explosion. Miss Myers compared the girl's power to the fury of a supernova. Her species, the Fleshkind, could manipulate electricity and electrical items. Sky had this ability to do this by laughing or crying. Upon being primed, Sky exuded an orange aura and could shoot powerful electrical pulses from her hands, far more powerful than those of the rest of her species. After absorbing the energy of a nuclear power station, Sky short circuited and lost most of her power, only retaining a small, unconscious ability to manipulate electricity (TV: Sky) as well as a sensitivity to electrical fluctuations. (TV: The Man Who Never Was) She also has enhanced senses on par with Luke Smith's. These senses allowed her and her adoptive brother to see the glitch that ousted Joseph Surf as a hologram. Also, due to not being human, she was immune to the effects of the curse of Hetocumtek placed on Clyde Langer. (TV: The Curse of Clyde Langer)
Her intelligence and learning capacity was beyond human as well. Not long after the defeat of Miss Myers, she enrolled at Park Vale with Clyde and Rani. She did not show signs of struggling in class, indicating she may have been given a crash course by Mr Smith of what she should have learned by her physical age in order to make school easier for her, showing her ability to learn lots in a short space of time.
It should be noted that it is possible that pre-adolescent Fleshkind only have a low level control over electricity. It is possible that as Sky grows, her powers will re-develop to normal Fleshkind level on par with her "mother", Miss Myers.
Behind the scenes
In the intended final story for series 5, The Battle of Bannerman Road, Sky would have been revealed as a "child of the Trickster" who had been given to Sarah Jane as part of the Trickster's scheme to conquer Earth with chaos. She, herself, would have become like the Trickster. Russell T Davies noted an interest in the horror of the Trickster's mouth and lack of eyes on a child. (DWMSE 32) A short story released for the Doctor Who: Lockdown! event, Farewell, Sarah Jane, was told from the point of view that this story had still happened with Sky "manifesting in her human form" to Sarah Jane's funeral.