Elizabeth Afton is the daughter of William Afton. She is also the girl who died in Circus Baby's Pizza World, as Circus Baby notices she is alone, lures her closer with ice cream, and then attacks and kills her.
Elizabeth Afton has long blonde hair, brushed straight doan, and a ribbon in the shape of a bow in her hair. She has pale skin and green eyes. She wears a magenta top, blue skirt/shorts and dark grey shoes.
Elizabeth appears in the Sister Location Death Minigame. After the blue-eyed Circus Baby gives all the children cupcakes, the player can obtain an ice cream from the end of the map. Then the player must go back to the start. Upon reaching the start, Circus Baby will drop the ice cream and Elizabeth will walk towards it. When she is close enough to Circus Baby, Baby's eyes will turn black, she will open her stomach and pull Elizabeth in using a claw from her stomach while emitting a horrific scream.
The actual event from Baby's perspective takes place at a birthday party, but the events are basically the same.
She is also mentioned in Freddy Fazbear's Pizzeria Simulator's Completion Ending. After Baby finishes her monologue about the player's job being a gift for her and the other animatronics, Cassette Man cuts her off and says this.
"I'm sorry to interrupt you, Elizabeth. If you even remember that name."
This seems to confirm that Circus Baby's name before her death was indeed Elizabeth Afton.