Evans bled to death in the kitchen of his home in Pantyffynnon Road, Ammanford, after the attack on January 22.
A Swansea Crown Court jury heard that Williams' brother Wayne, 16, and her mother Julie Williams are both key prosecution witnesses in the trial.
Williams, the mother of a young baby who lived at the time in Pembrey, near Llanelli, denies a single charge of murder.
She sobbed silently into a handkerchief as the full details of the case against her was outlined to the jury, reports Wales Online.
Elwen Evans QC, prosecuting, told the court vivid recordings from the scene, which allegedly capture incriminating background comments made by Williams.
She said Williams had stabbed Mr Evans in the chest and the arm, cutting an artery in his arm from which he bled to death.
She told the jury that brother Wayne Williams had witnessed the stabbing and later gave police a detailed description of what he had seen.
Mother Julie Williams had not witnessed the attack, but frantically fought to save her boyfriend who had quickly lost consciousness.
"You are not funny now, are you?" Williams is allegedly recorded saying as Mr Evans lies bleeding to death in the kitchen.
"I've done it. I have killed him, mam. I'm going to eat him mam, for us. I'm going to kill him and eat him up."
Ms Evans said that when police arrived on the scene an agitated Williams was in the back garden of the home and had to be restrained by a Taser.
She was arrested and taken to a police station where she told officers: "I'm glad I ripped his head off. I am glad I killed [him]."
Later she is told that Mr Evans has been officially pronounced dead and adds: "Good. I am glad he is dead. He will never hit my mother again.
"Bernard is dead because I killed him. Bernard deserved it. I have basically said I am guilty and Bernard is dead."
Ms Evans added: "As you will hear, that sort of comment, to the effect that she is pleased with what she has done, is a theme that she continued using throughout the hours and days following the killing of Bernard Evans."
The trial, which is scheduled to run for up to three weeks, continues.