By Julian Linden

LONDON (Reuters) - After being at the centre of a disputed doping case for years, Jessica Hardy has learnt the hard way about how to bottle her emotions, but just one look at London's Olympic pool was all it took for her to lose control.

When she walked into the Aquatic Centre and laid eyes on the sparkling blue waters where the Olympic gold medals will be won, she broke down and burst into tears.

"I couldn't help it, I just started crying," she told Reuters. "People were looking at me and wondering what was wrong and some of my team mates were filming me.

"But after everything that I've been through over the past four years, to finally arrive at the Olympics, it was just pure happiness."

Hardy qualified for the last Olympics but never made it to Beijing after she was told she had tested positive for the banned steroid clenbuterol at the 2008 U.S. Olympic trials.

The offence normally carries a two-year ban but the Californian was given a reduced penalty because of the unusual circumstances of her case.

She was able to prove that she taken a nutritional supplement that had been contaminated by the manufacturers but the case was far from finished.

After withdrawing from the Olympics then serving a 12-month ban, Hardy was then told the World Anti-Doping Agency (WADA) had lodged an appeal against her penalty, demanding that she been given a two-year penalty and banned from competing at the London Olympics.

The case was only resolved last year when the International Olympic Committee and the Court of Arbitration said she had served her punishment and could compete in London if she qualified.

"It wasn't that long ago that people were telling me I literally couldn't come here, so to actually be here now, it's awesome," she said.

"So I'm going to give it my best shot and fight as hard as I can to help the team and enjoy myself as well."

Hardy's experiences changed her whole perspective, not only on swimming, but on life and the justice system. And it toughened her up. Throughout the ordeal she trained harder than ever, determined that she would make it to London.

Then, another setback.

She entered a handful of events at the U.S. Trials but was pinning her hopes on qualifying in the 100 meters breaststroke, where she is the reigning world record holder.

Only the top two finishers from each event get picked for the Games, but the 25-year-old could only manage third and her heart sank.

But just when it seemed all was lost, she drew everything she could from the frustration and torment she had endured through her legal battle and swam her remaining events like a woman possessed.

She surprised herself by qualifying in the 50 and 100 meters freestyle, beating a crack field of sprinters in races she does not normally go in, giving her four events for London, with the addition of the relays.

"It's been quite a journey just to get here," she said. "Nothing that has happened was ever what I expected to happen but I'm here now and I'm ready.

"It's been a bit of a steep learning curve for me, having to prepare for freestyle, but I've been able to tap into all the other freestylers on the team and really work on little things to improve my technique."

(Editing by Alastair Himmer)