Poor you. I thought this was over and done with. It would seem that the aftermath of the abuse is turning out to be worse than the abuse. Just tell your son to tell the truth, and that if he doesn't know the answer to something that he should say, "I don't know." That is very important since they may try to manipulate him. I presume you will be in the courtroom. If there is any badgering, put a stop to it.
Yes, I agree that the attorney prosecuting the case should work with you and even meet with your son beforehand. I think it is terrible that he must go to court like that. Geez, insult on injury for a child victem of violence! But if it gets her to be found guilty, it is worth it. I'd make it really cool as Sandman says, practice it, talk about how cool it is, keep yourself and what you say in front of him positive and let him know that you are doing it because she did the wrong thing to him. But talk to that prosecutor about this.
Good luck and I just find it quite horrible that your son had to go through her abuse.
I can see why you would be worried - of course, he could think the whole thing is really cool? I would certainly talk to the prosecutor and get their feeling for the whole thing. Perhaps a rehearsal could be done? You certainly don't want to walk in there cold with no idea of what is going to happen. Also, did you get subpoenaed or was it for both you and your son? If he wasn't, I don't think he would have to go. Simply asking you to bring him may not be the same thing as forcing you to bring him. Here again - talk with the prosecutor. Keep us posted!!! Hang in there!