When Nikki is first introduced in the comic she doesn't speak at all. All anyone knows of her is that she possess incredible power. Her silence and lack of response leads the team to believe she is autistic. Among the children that appeared at Titan's Tower Nikki has proven to be the most powerful, even managing to take on the entire Titans team on her own.
When the children lose their friend Kevin, Lilith Clay steps in to act as a grief counselor. Because Nikki doesn't speak, Lilith attempts to communicate with her telepathically only to find out that Nikki's not alone inside her own mind. The presence in Nikki's mind causes her to lash out and destroy her room. The thing in her mind is diagnosed as a psychic parasite and the team work together to restrain Nikki to free her from it. Lilith succeeds in freeing Nikki and is surprised to find a man emerge from the child's mind.
The man is called Breegan and was pursuing an anarchist from his world. Nikki at the time was on vacation with her family. The arrival of the anarchist disrupted the environment, killing Nikki's parents and putting her in a state of shock. When Breegan tried to communicate with her by creating a psychic link something went terribly wrong and he then in turn became trapped within her mind. Nikki's relatives sent a rescue helicopter to find her when her family did not return and Breegan tried to signal for help using telepathy. His doing so made people believe that Nikki was a metahuman and they handed her over to D.E.O. mistakenly.