From Malcontent's pen n_n:

Being part of the survivors of the Canterlot Disaster, Scootaloo lost her right arm immediately when a magical wave hit her and her group of friends as they stood near the stage. After the strike, the world went black for the purple haired teenager.

The next she knew she was waking up in the hospital inside Equestrian City. Trying to move she winced and looked down to see the apparent injuries caused by the exposure to the blast wave. It didn’t take long before Scootaloo began to complain of a constant whistling in her ears that became unbearable after prolonged consciousness. The only way she found to cope with it was to be sedated, which the medical professionals began to worry would lead to serious complications.

Jumping from specialist to specialist, she became lost in the health care system, a system that was already trying to deal with regular casualties and injuries on top of all the new magical ones. Finally Scootaloo was told there was no cure and to simply learn to adjust.

Left with desperation due to any hope of silence appeared gone, she received word there was a scientist experimenting on magical injuries. There was only one catch, it was outside of the country in the Eastern Empire. A brief moment of whistling was all that it took for her to go and get on the next boat to Sombra’s lands.

Once there, she was escorted through processing and countless hoops to jump through to apply for citizenship. Scootaloo was passed from one scientist to another, each one giving their approvel that she was indeed beyond their abilities, sending her further and further up the testing line. Just when she began to lose hope, she became the next experiment of Professor Midnight, formally known as Twilight Sparkle.

Little care for her safety was given but Scootaloo was willing to take all the punishment needed to make the wind stop in her ears, filling her head endlessly. She gave herself fully to Midnight’s experiments and after several weeks of endless prodding and poking, slicing and grafting, she awoke one day to golden silence. The genius that was Professor Midnight had cured her and, better still, had harnessed the magic inside her to power a prosthetic arm.

Having not expected her to survive, Midnight was amused and continued to tinker with her latest toy. Finally fitting Scootaloo with earpieces and routing the wind through the mechanical arm, Scootaloo became fiercely loyal out of gratitude and assumed the role of assistant and bodyguard. Now she protects Professor Midnight from any would-be threats or lunch, whichever she requires.
Inspired by several elements the most obvious people tell me is the winter solider. So I told Moon to go for the references this time. Turned out pretty good I think 😉

If you wish to pass around the Project's Wiki or the official site Equestriancity.com, you're all welcome n_n.