Developing a strong relationship with the Order's Grand Master, Robert de Sable, she was eventually given a high rank in the Order. In 1191, after the Assassin Altaïr Ibn-La'Ahad killed eight Templar agents spread throughout the Holy Land, she was assigned by Robert to act as his decoy and thus trick the Assassin into assailing the wrong target. The plan was a success, and Altaïr spared Maria's life. However, Robert was ultimately killed shortly thereafter, and Armand Bouchart took over as Grand Master.
Bouchart did not favor Maria, however, and did not find transport for her when the Templars moved to Cyprus. Planning to find her own way there, she was defeated and captured by Altaïr before she could do so, as the Assassins had attacked the Templars' fortress in Acre. Blaming Altaïr for ruining her reputation in the Order, she was taken with him to Cyprus and forced to help him take down the Templars.
Unwillingly giving information to Altaïr and escaping her captors several times, Maria began to realize that the Templars' ambitions were not beneficial for humanity, and slowly grew closer to Altaïr. Eventually, she and Altaïr infiltrated the Templar Archive in Limassol, where she went ahead of the Assassin and faced off against Bouchart alone. Though she was defeated, Altaïr was able to defeat the Grand Master and help Maria get out of the crumbling Archive.
Maria then followed Altaïr to the Assassins' fortress in Masyaf, where she settled down with Altaïr and had two children with him. Several years later, Maria, Altaïr and their son Darim went on a journey to assassinate the Mongol leader Genghis Khan.
Maria was killed in 1227, during Abbas Sofian's coup d'état against her husband.