Actually, when a passenger asks to "pull over and let me out" and the driver does not, that's illegal confinement.
And, to make matters potentially worse, if the two did not previously know each other, and the driver refuses to let the passenger out at any time, that could be legally construed as kidnapping.
Of course, in this case we're talking about only one person's word against another without witnesses to anything truly wrong. For all anyone knows, she could have been messed-up on drugs, paranoid, etc.
If the police ever do find the driver, they have a right and obligation to question him, but certainly not to arrest him unless he say's something incriminating.
I'm no lawyer(yuck if I ever was!) but just stating my gut-feelings on this case.