What happens if the DA's office mailed a letter saying they were ready for trial but there is not court date or anything?

My daughter was shopping with another girl. The other girl stole a lot of items from the store. As they left the store in my car, the police pulled her over, had her exit the vehicle and asked if he could search it. She agreed. They found the stolen items in the car. The passenger admitted (after a while) to stealing them. The girls were released. The passenger was then arrested a day later. My daughter received a phone call three days later and was asked to come down to the station. They were arresting her for possession of stolen property. She went to court and while we were there, the clerk told her she didn't have her on the docket, he showed her appearance ticket and signed her in. The judge called him up and said he had no paperwork on her and she was free to go it was her lucky day. She didn't enter a plea at all. He never asked. We left and had not heard anything until yesterday. How can they do this? Shouldn't they have had all the necessary paperwork that day? She was read her rights when they brought her in to finger print her. She didn't steal anything. She was questioned at the car and asked if she knew if the other girl was stealing. She didn't answer. Isn't that her right to remain silent?