Saint Monica was a woman reportedly born to ghouls in the Great Lanta. She exhibited none of the ghoul condition, so many attributed her birth to be an act of God. She gave birth to a son much later in life, named Ehran.
Eventually, slavers raided Great Lanta and Monica was separated from Ehran. She went from slave master to slave master, never giving up hope that she would see her son again. Eventually, she found her son - as a slave owner himself. He blamed her for the childhood he had lost to the slavers, and beat her daily. Yet, no matter how hard he beat her, she would simply smile and say "I forgive you". This ate away at Ehran, until one day when he realized the errors of his ways and freed all of the slaves he owned.
Saint Monica appears to have several strong similarities to the real Saint Monica. While not a child of ghouls, Saint Monica was a mother of a wild and sinful son, who she continued to attempt to convert to Christianity. Her son would later become Saint Augustine. She is the patron saint of surviving abusive marriages, disappointing children, victims of abuse and converting relatives.
Monica is only mentioned in Fallout 3.