Shauna was born in Dublin, Ireland to Dr. McShane and Sandra McShane with severe muscle deficiencies. Doctors told her parents that she was going to die when she was 4 and a half. Her father, being a doctor himself, refused to accept this and decided he'd figure out his own way to cure his daughter. Shauna's mother couldn't bear to see her husband try so hard to cure the little girl, so the two constantly argued and eventually divorced. Eventually, Dr. McShane reached a breakthrough and found a way to "cure" his daughter. By this time, she was clinging to life by a thread, so he decided to concentrate the dosage. Shauna was progressively getting better with age, but she eventually found the meds were working too well in a manner of speaking. One day, when she was 9, a bully stole her crayons, so she punched him and he flew all the way across the classroom and made an impression in the wall. The incident was quickly covered up when her father wrote a huge check to the school and another huge check to the boy's family. Dr. McShane analysed Shauna's blood and realised he had created a super human. He then began treating his daughter like a science experiment rather than, well, his daughter. He experimented with her to see if he could give her any other abilities. Out of the thousands he tried, most of which made the girl sick, he only successfully gave Shauna two other abilities. Super energy and long-lasting endurance. The drugs and experimentation also gave her a very bad temper. At the age of 10, Shauna's father decided to take his studies to America, possibly because they had gained such a bad reputation in Ireland, so the family moved to Gotham City, where Shauna attended the Gotham Education Facility for Privileged Children, which she often calls the "public school for rich twats". Once she got there, she had heard about the super heroes known as Batman and Robin. She immediately wanted to be like them, but knew she didn't have "a chance in hell". Eventually, at the age of 12, Shauna started entertaining this line of thought and began doing vigilante missions while wearing a motorcycle suit and a helment to conceal her idenitity. She often borrowed a motorcycle that belonged to a friend who she trusted to keep her secret. While attending school, Shauna found herself in fights on a daily basis with the "school douchebag" Damian Wayne. The two constantly fought with each other and insulted one another. One day, Damian's chauffeur was detained to tend to the limo's sudden breaking down. Damian was forced to stay on campus until other arrangements could be made to pick him up. Shauna took advantage of this and taunted him, but after talking to him for a while, they both realised that the other wasn't all that bad. Slowly, their friendship grew and the two began dating when Shauna was 13. The two lost their virginity to eachother that same year. Eventually, at a robbery that the Joker caused and Batman and Robin manage to intercept, Shauna confronted him, having wanted to do so since she's heard of him, but it backfired when he sprayed toxic mace in her face with his flower. Robin used a salve to save Shauna's eyesight, and in doing so, discovered her idenity before revealing his own. When Talia Al Ghul sent the Heretic to kill Damian, Shauna tried to stop him, but in unsucesfully doing so was stabbed so many times that she slipped into a coma from blood loss.
As RobinEditWhilst in the hospital, Shauna was visited often by Batman, who felt personally responsible for the attack. Once she recovered, she visted Wayne Manor, where she was led to the Batcave by Alfred and Batman offered her a position as the 6th Robin. Shauna eagerly accepted, despite multiple warning about how much hard work was involved from Batman. She saw this as something Damian would have wanted.
Shauna quit being Robin of her own accord and left Gotham City. After being briefly trained by Selina Kyle, he ran away from home, moved to New York City and tried to scrape up a new life there. Eventually, she tailored a new costume. This is when she began calling herself "Catgirl", which is the identity she is most known for. She would do things like stop robberies and what have you. Once she joined the Teen Titans, she got along considerably well with everyone except for Best Boy, who is annoying, Raven, who is too negative, and Starfire, whom is just plain weird.
After a series of mental breakdowns, at the age of 17, Shauna decided to end Slade/Deathstroke's targeting of the Teen Titans by striking a deal with him and becoming his apprentice. She made it firmly clear that she was only his apprentice as long as he didn't hurt the Teen Titans. If he did that, the deal was off. During this time, Shauna changed her alias from Clamp to Steelrose on account of the fact that Clamp was her hero name and she was no longer a hero.