Mama and Lockne were genius twin sisters born with DOOMS that gave them the ability to communicate with each other across the world. Together, they each made half of the Chiral Network: Mama, the hardware, and Lockne, the software. Their equal genius and close bond was so great that many believed they were the "same person in two bodies."

However, Mama's ovaries were unable to fertilize and Lockne's uterus was incapable of carrying a child to term. While both were initially accepting of these circumstances, Lockne eventually fell in love with a Bridges member and wanted to develop a relationship with him. However, he died in an accident, leaving Lockne depressed and wanting to kill herself.

Mama could feel this, and wanting to help her, proposed to Lockne that they should "have a baby." Using the deceased's sperm, Lockne's eggs, and Mama's uterus, the two sisters were able to create Lockne a child that would be carried to term by Mama. However, during a terrorist attack, Mama was crushed under the rubble of a hospital while waiting to get a cesarean section. She inadvertently survived by "giving birth on the other side", resulting in the baby manifesting as a harmless beached thing.

Stuck for days drinking timefall, Mama was eventually rescued by Bridges, but could not leave the hospital, as she and Lockne's daughter were tethered to the accident site. In addition to this, Mama was no longer properly living, and hid this by leaving one of her cuff links off of her wrist, effectively hiding her vitals.

Furthermore, Mama's bond to Lockne was severed, and in both fear and shame for what happened, Mama cut herself off from all communications with her, alienating the twins apart.

Source: https://deathstranding.fandom.com/wiki/Mama