You were rescued from a deadly base consisted of human experiment on scientists, but from that you had inherited powers like telekinesis. telepathy, photon blasts and etc. When you were rescued from the leaguers they thought it good to join you into the Young Justice team who were new budding heroes despite you being slightly older than Kaldur too (who was eldest on team)

The Young Justice team were in the Mount Justice lazing around in room which consisted of Robin (Dick Grayson), M'gann, Superboy, Kaldur, Artemis, Kid Flash (Wally West)

As the zeta tube speakers turn on and you enter wuth other leaguers

Man of steel: "She's the new addition to team"

The Dark Knight: "We rescued her from a human experiment base recently, she has shown good signs to join the team"