She is a serial killer and black widow, known for killing all of her husbands and taking their fortunes for herself. Debbie is a sneaky, genius, psychopathic and manipulative seductive woman, marrying Fester only because she thinks he is a rich bachelor, planning to kill him and take his inheritance.
After she strapped the Addamses (except Pubert) to electric chairs, she then used slides to tell how she came to be. On her tenth birthday, she killed her parents, Dave and Sharon Jellinsky, and set the house on fire because they did not buy her the Ballerina Barbie doll "in a pretty pink tutu" she wanted, giving her a Malibu Barbie doll instead. However, despite all of that she kept her father's surname.
When she grew older she killed her first husband, a heart surgeon, with an axe (reminding Grandmama of her youth) because he was too busy to dine with her ("...the Pope had a cold..."), and ran over her second husband, a senator, with her car because he would not buy her a new Mercedes-Benz (as they had "to set an example" during the recession). She tried to kill the Addams family because she thought they didn't love her enough.
Fester begs Debbie to just kill him and spare the others, but she rejects his offer and flips the switch. Pubert saves his family by short-circuiting the wiring, sending the powerful current of electricity back to Debbie, which repeatedly shocks her until she is reduced to nothing more than a pile of ashes, leaving behind her shoes, jewelry, and credit cards.
She is buried in the Addams Family cemetery. At the end of the movie, a hand (presumed to be Thing) reached out from her grave and grabbed Joel Glicker's arm, demonstrating Wednesday's technique for scaring a hypothetical future husband to death.