Kelsey was attacked by thugs who tried to rob her. Kelsey's husband was too afraid to act against the thugs; however Kelsey tried to fight back, which lead to her becoming physically scarred. The event led to Kelsey's marriage breaking up.
Kelsey began to bring her children up as a single mother, her son idolizing heroes such as Captain America. During a battle between the Wrecking Crew and the Avengers, Captain America was knocked unconscious. Kelsey grabbed the Captain's shield and used it to deflect an attack from Thunderball. The impact of the attack killed Kelsey.
Seeing her heroic act, Brian Braddock gave her the opportunity to live again and the choice to choose between the Amulet of Right and the Sword of Might. Kelsey chose the sword and she was transformed into the new Captain Britain. However, as the sword represents the path of violence, Brian informed her she could never reveal herself to her children.
Kelsey accepted a position on the Avengers, helping them to defeat Morgan Le Fay and to stand up against the new Invaders team. Kelsey even protected Captain America again, this time from a crazed She-Hulk, however this led to Kelsey being hospitalized. After recovering, Kelsey left the Avengers and returned to England, taking up the name Lionheart. Recently, Kelsey helped the Excalibur team that was led by Brian.