From an employee perspective who has had workmates have things stolen by a work experience student (I didn't work on the day this student worked) I would definitely report it to the police and leave it with them
Why? Because who is to say that she wont do it again? Would you feel worse finding out she had stolen from new work mates or reporting her to the police?
There will be no embarrassment or shame from her once she has left your employ. Do you know 100% that she has not done this before?
Another, more personal level, my sister stole money form her first job. She was caught red handed, they let her off. She then stole form her second job but because they did not know about her previous theft they also just let her off with the sack. She stole form her 3rd job and was lucky to not get reported as it was only after intervention from my mother they did not. Her next job in a large insurance firm on the catering department meant she had a lot of authority. She was responsible for ordering food etc. She used to bring home joints of meat, money, veg etc etc all stolen. Yet again she was not reported to the police - because of this she has never paid restitution for any of her thefts
Sorry, went off on a tangent there but it is just my opinion that you have a duty to future employers and employees to report her