After Athan is born, Magdelena is assigned to be one of Athan Cole's four Guardians when he is transported back in time. Her role, in addition to protecting him, was to be a "Shaper" who would guide him to become the Witness, which the Army believed was pre-ordained through the Witness's own writings.
Magdelena is killed by Railly, who activates the self-destruct on her splinter suit after a brutal confrontation during the splinter team's raid on the safehouse in 1953.
Magdelena was an utterly devout and fanatical follower of the Army of the 12 Monkeys. She was willing to self-destruct herself several times in order to protect the Witness and his cycle.
She felt extreme pride and ownership over being given the responsibility to shape Athan's future according to what the Army believed must happen in his cycle. She even resented Railly for being the biological mother of Athan, taking several opportunities to gloat that her role as the Shaper was the larger part of being a mother than gestation and birth. When Sebastien, one of the Guardians charged with Athan's education, shows independence and doubt in the his duties, she threatens him physically.
Magdelena was also merciless and unremorseful about killing in the name of the cycle and protecting the Witness. This was evidenced in her killing Arianna (one of Railly's attendants on Titan) after Arianna was found to help Railly escape from Titan in a possible future. She would also perpetrate the murder of dozens (and possibly hundreds) of grieving and lost individuals throughout history who attended the 12 Monkeys recruitment meetings.
As the Shaper, she was domineering in pushing Athan to become who she believed he was fated to become, going so far as to threaten him when he started to resist that vision.
She is shown to be a powerful fighter, able to handily take on Railly during their confrontation in 1953.