Show up at the courthouse at least a few hours before your case is set to be heard. Doing so will maximize your chances of getting in to talk with the prosecutor and will minimize the chance that the prosecutor will already be in court arguing another case.
Find out where your case is being heard and in front of which judge it will appear. If you don't already know this information, simply ask the security personnel at the main entrance where you can find out about this information. The security guards are generally very helpful sources of basic, generalized information. Use them appropriately.
Head in that general direction. Somewhere in the vicinity of the courtroom there will be a room set up for attorneys and prosecutors to prepare and relax. This is the room you're seeking. If you can't find it, find a court clerk or attorney and ask them where the room is located.
Know what to say. Be honest with her and upfront about all the issues, while simultaneously trying to persuade her that you are a good person who deserves another chance.