Little is known about the lonely life of this fourteen year old girl, other than the fact that her mutation causes people to be totally unaware of her presence and for those who do rememeber her, let them forget. This is because of a psychic mental block she constantly emits and can't shut down herself. In a sense she does not exist until she met Alex.
She lived in a house whose inhabitants were unaware of her presence so she effectively helped herself to their food and possessions. One day she was caught in an accident involving a foiled jewel heist. This accident was foiled by Alex Hayden who could see her and remember her it is unknown why Mary's power had no effect on Alex as a result of this, she became instantly infatuated with him and follows him around everywhere. Mary has even decided that Alex is now her boyfriend even though Alex is Creeped out because she is too young for him.
Mary was used as an instrument in the takedown of the Four Winds by using her powers to get into places that a normal person could not because they would been easly noticed and taking pictures of the members families. This gave the Four Winds proof that Agency X could get into anywhere any time they wished to. Mary is currently sticking by Alex and his assisstant Sandi Brandenberg's side and is willing to help Agency X any way she can any time.
Mary Zero has been confirmed as depowered by SHIELD computers as a result of M-Day. Though her whereabouts are unknown she presumably enjoying her new life because her powers made her invisible to everyone and the fact she wanted attention and Companionship during this time made her grately full she lost her powers