Sasha was born into a family of experienced thieves based in Mistral. Her parents were a duo of expert infiltrators who would take any job they could find, no matter how difficult or how high the security. When their daughter was born they saw an opportunity. They were both beginning to get old, and their skills were declining. But this new child could be raised as an even better thief than the two of them put together. She was trained from a young age to use a variety of tools and weaponry to prepare for her job.
Sasha began with a very narrow view of the world. Her parents made sure that she didn't leave their sight, and she was only allowed to meet with other people very occasionally, in case she let slip any important information. She first began missions at the age of fourteen. She began with comparatively simple tasks; stealing from low security areas, mapping out potential targets, etc. As she had been trained since she was extremely young, she was unable to tell that what she was doing was bad. All of her education revolved around fighting and stealth techniques.
It all went wrong when Sasha was sixteen. An opportunity arose that was impossible to miss: a shipment of valuable cargo being transported from Mistral to Vale via airship. At first it seemed like it would be easy money; take out any guards, take the object of importance and flee using a personal flying craft that would be piloted by Sasha's parents. However the plan didn't take into account the fact that others had noticed this valuable opportunity, namely the White Fang. They were tasked with destruction of the ship and the cargo it held. Sasha entered the ship and, as planned, breached the cargo hold. She quickly found the object; an extremely valuable piece of military equipment. The plan was to sell it off for a large sum.
Unfortunately the first White Fang charges went off before Sasha got out. Seeing the explosions from afar, her parents flew in to save her. As the airship began to lose altitude Sasha was retrieved and loaded onto the smaller craft. However the White fang would not allow survivors. Firing shots at the thieves' ship as it flew away they managed to damage it. It too began to fall, but the pilots managed to fly it to Vale before crash-landing. Only Sasha survived the crash, though with heavy head injuries as well as multiple other deep wounds over her body. She was brought to a nearby hospital as quickly as possible.
She came round a few days later, however the damage to her head and loss of blood caused a severe case of amnesia, causing Sasha to forget her history and identity, though retaining her skills in combat and infiltration.