Bethany was born in 1961 (which makes her 35 during the events in Dogma), and was raised as a devout Roman Catholic. When she was five years old, a neighborhood kid named Bryan Johnson urinated in her hair (Bryan died of leukemia two years later). She didn't tell anyone about the incident with Bryan Johnson, until it was revealed to her by Rufus 30 years later.
Upon leaving high school, Bethany attended Carnegie Mellon University in Pittsburgh with her high school sweetheart, Brett Waits. Free from her parents, Bethany and Brett have sex on a regular basis, until Bethany gets pregnant sometime in 1981. After an argument on whether or not to have the child with Brett, Bethany gets an abortion. She tells him, however, that she had a miscarriage.
Upon graduating from Carnegie Mellon, Bethany and Brett get married and attempt to start a family. However, Bethany had an infection inside her uterus stemming from her abortion years earlier, making her unable to have children. Upon finding out about this after Bethany confesses to Brett about what had really happened, Brett divorces Bethany and some time later, marries another woman.
While Bethany is talking to her mother about her personal crises (i.e., losing Brett, unable to have children), Bethany loses her faith in God. Shortly afterwards, Bethany settles in McHenry, Illinois and works at an abortion clinic.
Azrael, a former muse-turned-demon, tricks the two fallen Angels Loki and Bartleby into going to a church celebrating its centennial in New Jersey in order to exercise the plenary indulgence law in Catholicism. By entering the church, both angels' sins would be automatically forgiven, this making them eligible to return to Heaven once they revert to human form and die. However, what they don't know (but Azrael does) is that the universe and creation is based on God's infallibility and should the angels reverse God's decree of not being able to return to heaven, existence would end instantly.
Before that, Azrael sends the Stygian Triplets to incapacitate God, who was down on Earth in a body playing skeeball to keep Him from intervening. Metatron then appears before Bethany and orders her to go to New Jersey to stop Bartleby and Loki from entering the church. She also gets two helpers in the form of drug dealers Jay and Silent Bob, who rescue her from the Triplets when Azrael sends them to kill her. Thinking that they will get laid if they help her, the two stoners agree to come along. However, Jay messes up Bethany's car along the way because he can't drive a car with a manual transmission.
Furious, Bethany decides to return home, but stops when a third helper falls (literally) from the sky. Rufus, the little-known 13th apostle, decides to help Bethany in her task. He tells her about his campaign to gain recognition as Jesus' last apostle and to correct Jesus' ethnicity in the Bible. Bethany is still cynical, but starts to come around when Rufus reveals to her the incident with Bryan Johnson.
Later, they find Jay and Silent Bob inside a strip club, along with Serendipity, a muse who has a case of writers' block. The Golgothan shit demon, Hell's chief assassin also finds them, but was defeated when Silent Bob sprays air freshener into its face, knocking it over. With time running low, Bethany and her companions board a train for New Jersey. Through a twist of fate, Bartleby and Loki are also on board. While Loki is getting high with the two stoners, Bethany and Bartleby are talking, with neither person knowing who the other really is.
While Bethany is drunk, she lets slip about her mission, which greatly upsets Bartelby. The situation then intensifies when Rufus recognises the two angels. After a brief scuffle, Bartleby and Loki are thrown off the train by Silent Bob. The group abandons the train and while camping in the woods, Rufus reveals to Bethany that she is a distant relative of Jesus Christ. Bethany breaks down, but Metatron is there to explain why didn't tell her about her lineage the first time they met and to help her come to terms with her new identity. The group resume their journey and find Cardinal Glick, in an attempt to stop the rededication ceremony. Glick refuses to do so and orders Bethany and the others to leave.
Inside another bar, while Bethany and the others contemplate what they should do, Azrael appears, as does Serendipity. The former demon and the Triplets holds the group hostage while at the rededication ceremony, Bartleby and Loki disrupt the festivities, Bartleby having completely snapped and killing everyone. Silent Bob uses a blessed golf club (pilfered from Glick) to kill Azrael while Bethany, at Serendipity's suggestion, blesses several sinks filled with water, allowing Jay, Rufus and Serendipity to eliminate the Triplets.
Upon arriving at the town, they find Loki, wingless and human, not to mention drunk. Bartleby appears and despite Loki's efforts to stop his old friend, Bartleby guts Loki, killing him. As Silent Bob, Serendipity and Rufus attempt to restrain Bartleby, Jay lets it slip that John Doe Jersey - God in human form - is in the hospital across from the church. Ordering Jay to stall Bartleby and taking Silent Bob with her to the hospital. Bethany finds the comatose man and pulls the plug on him, cutting off his life support and releasing God from the body. However, she is mortally wounded in the process and dies.
Silent Bob finds her body and takes it back to the church, where Bartleby had been killed by God. God then revives Bethany and for her efforts in saving existence, God allows her to have a child. God, Serendipity, Rufus and Metatron all return to heaven, leaving the mortals on the church steps.