Mireille Forshaw was a Battlefield Commander of the Imperium of Avalon's High Command, gaining her position by proving to be a veritable prodigy when it came to Battlefield Command.
When she first entered the Systems Alliance Military Academy, her impressive skill was noticed by the Emperor, who tested and prepared her extensively, until, when she graduated, he transferred her to High Command, under the rank of Battlefield Commander.
However, she would meet an untimely end in 51 AIA (2046 AD) when her forces, deployed to the fringe colonies in the Centralis Galaxy, were ambushed by Moebius Corps forces. Her efforts, however, allowed her forces to hold out long enough for reinforcements to arrive from the Alpha Milky Way Galaxy, with her dying just as reinforcements arrived and found her.
However, rather than being sent into the afterlife, she instead was pulled into the Wasteland, where, after taking the time to recover from her ordeal, she began gathering Avalonean forces and civilians from across the Wasteland in an attempt to return home. Her efforts would soon draw the attention of the Khonem Confederacy and the much more benevolent Girene Empire.
Mireille is a serious individual, but is not without compassion and kindness. While willing to put her ideals aside to finish the mission, there are some lines she won't cross, and others it would take extreme circumstances for her to cross.
Despite all the praise she gets for her skills, Mireille is insecure, and worried that she is only appreciated for her tactical prowess, which, while humanly possible, is still nothing short of extraordinary. According to her, no one has ever complimented her on anything else, and as such thinks her skills are her only strong point. Her possessing the Emperor's favor seemed to only fuel this belief in her.
Mireille Forshaw is a Biotic, that possess the experimental L8R Implant, designed for a wide variety of uses. Mireille has training as a Vanguard, although she also had limited Infiltrator training, before her Biotic Potential was discovered. She has amazing physical dexterity, lending well to her original choice as Infiltrator.
Mireille Forshaw has all the basic abilities of a person sent to the Wasteland: as in, she's been affected by the Turritopsis Effect, the Sullivan Effect, and the Quartermaster Effect (the Ramsay Effect had no effect on her, since she already breathed an Earth-like atmosphere).
Mireille possesses an extremely keen mind, allowing her to out-think all but the most experienced AND skilled opponents.
While seemingly superhuman, however, her mental abilities are in-fact within what is humanly possible, so supernaturally-augmented or inhumanly-experienced generals (such as Asari Matrons (and older), older Klingon Generals, or Protoss Executors) can outmaneuver her.