Seems to me that there are really sick people on both sides of the prosecutor's desk.  Certainly her cooperation helped the case but unless she was an abused and a totally dominated woman with an IQ of 50, she knew what she was doing.  That makes her an accomplice.  Guilty, by her own confession.  

So why the deal?  Politics most likely because by not prosecuting, a bed is not filled and money is saved.  This is our sad 'non penal' system.  The cry, 'the system is full'  reduce the population, revolving door, repeat offenders, all of these relate to the same base issue.  The system is broken!  The rehab system doesn't work.  The wingnut Judges and Lawyers play right along with the namby, pamby, liberal society that just can't stand the icky thought of real punishment.

It does not help having a society that idolizes drugs and isn't smart enough to tell if they are a boy or girl.  That type of society just doesn't care about right or wrong.