I'm trying to figure out why someone from the jail is calling you. You're not his guardian. He's an adult. This makes no sense, sorry. It makes even less sense that she recommend that you right a judge. It is illegal for the judge to read anything you (or anyone else for that matter) writes to him unless it is filed with the court with copies to all parties (attorneys or individuals if represented by themselves). Since this mental health person is part of the jail system, she should know this.
If you decide to write a letter, simply send it to the PD's office with your son's name and case number. It will be given to the appropriate attorney and then filed. The PD can mention your letter at the hearing or even introduce it as evidence if he or she deems that would be the appropriate action.
Writing the judge directly is an act of futility. When he was a juvenile, you could do this so long as you copied all parties -- the laws for juvenile offenders is much different. He is now an adult facing felony charges. At the least, the judge will send the letter back to you. At the worst, he might pull you up for contempt charges and either fine or jail you.
Susan, you really need to tell the people at the jail to not contact you. This is your son's responsibility. Not yours. He needs to learn to sink or swim on his own. No matter how much you try to do for him, it won't ever be enough and it will not lead to success for him -- he really has to do this for himself.
Like an infant, you held him when he first started learning to walk. Once he was walking, you let him do it on his own so that he could start his road to independence. As a young boy, you held his bike as he learned to ride. Then you let him ride with training wheels; then back to holding the bike a little until he got used to no training wheels. You've held him up long enough. The training wheels have been removed -- as a matter of fact, he removed them himself when he left rehab after rehab without working the programs. It is time for him to ride alone, whether you feel he is ready or not.