While on a fishing trip with her family Mandy along with her mother, father and brother Joey, recieved super-powers from a meteor that crashed landed nearby.
Mandy was created by Chuck Austen and Ron Garney for their story arc, JLA: Pain of the Gods. Although Mandy is seen in issue #101 she isn't named until issue #106.
Major Story Arcs
JLA: Pain of the Gods
Mandy is playing outside when Superman comes to tell Mrs. Abernathy that he's sorry for her husbands lost. Then when the JLA come to talk the Mrs. Abernathy about Joey and his superpowers, Batman learns that Mandy has super strength like her father and brother. Later when Mrs.Abernathy goes to the home of Mr. Clinton the man she feels is responsible for her husbands death Mandy is brought along by the JLA to help stop her mother form making a grave mistake.
Later Mandy is present at the grave site of her father when Superman tries to apologize again. It is unclear if Mandy blames Superman for her father's death like Joey does or if she is too young to understand.
Mandy has super strength.