I think the ramifications of making false accusations (possible jail time) may be what Nifong has been holding over the accuser's head thus far to keep her from backing out.
Somehow I think it has to be more than that because of steps that NiFong has done....liking RUNNING to the Grand Jury. Best guess is that he wanted that particular judge.
It wouldn't surprise me if he's also holding charges over the head of her "boyfriend" as well, just to make sure she testifies. And if the "boyfriend" already has a felony conviction on his record (would that surprise anyone?), he could be looking at serious time. JMO