On February 28th, Kelly and her mother Shannon Gibbs were passengers in a car being driven by an NIS agent assigned to guard them.
A sniper later shot the unnamed NIS agent in the head, killing the agent instantly and eventually causing the crash that cost both Shannon and Kelly their lives.
A few months later, Gibbs tracked down the murderer Pedro Hernandez and killed him in revenge for Hernandez ordering the deaths of Gibbs's own family.
In Life Before His Eyes (episode), two alternate scenarios were presented regarding Kelly Gibbs alongside her mom Shannon. One, regarding Gibbs failing to avenge them, had Gibbs becoming a drunken recluse. The other, regarding their survival, had them discovering Marines at her doorstep, presumably to inform them that Gibbs had died in battle.