The island and the isolation had been really hard on her. She wasn't the type of person who enjoyed being alone, but she didn't feel safe with the wolf running around when Jack wasn't there. She felt sure that she would try to destroy the thing that was apparently a friend of Jacks, not to mention somebody who was traveling with them.
There were many things on that island that Kai didn't want to see face to face, fearing what she might do.
And she missed Jack. The constant companionship had been wonderful, Kai had grown accustomed to seeing her every day. First traveling to Electric City, then staying with her in the WMCA. It was hard to not see her friend and mentor even once in the whole time that they'd been stuck in the middle of a vast sea.
The truth was, Kai didn't trust herself without Jack handy. Jack knew everything that was going on, knew good ways to help calm Kai down. She understood that there was a kind of unshakable force inside that had to be fought against. That wasn't easy to explain, Kai didn't think she could do it again.
When she heard the pounding on the door, she looked up from the ball that she was curled in. The room was a little more comforting than the island, since it was made of metal and had her things in it. But it was still very lonely. At the sound of the familiar voice, though, Kai shot up and ran to make her greeting. She managed to get the door open, and then flung herself at Jack, not caring about anything else.