There's two options in my mind of what Reese's girlfriend will do. But she's a traitor either way.

- It's possible that she was telling the truth, that she bribed someone inside John's Organization to send her back, but now she plans on stopping John for some shallow, stupid reason. "He trusts machines too much," or something stupid like that.

- More insidious, she's completely lying. Skynet captured her during the assault she was injured in, and made a deal with her. Skynet would send her back, and she could enjoy the easy lifestyle of pre-Judgment Day, provided she kill John. She already feels betrayed, so it wouldn't be too hard to tempt someone like that. It also is a rather ingenious plan by Skynet, since John and Sarah are always expecting machines to come after them. If there is someone they know is human, they might drop their guard.