POssibly too late to do anything really but my daughter had the same thing happen except it was taken from our home when I wasn't around. . .
we called the police and filed a robbery complaint. Gave the police all the info including names and the serial number of the ipod (hers was one of the $400 vidoe ones that came out a couple if years ago so it was a "major robbery").
We (I) never heard from the police, but we heard through the grape vine that the kid was questioned. He didn't go to her school so there were no repercussions along those lines, but she was on the look out for him for a little while - just incase.
Anyway, it taught her to be a little more careful with her things and about who her and her friends let into the house.
If you have the box (serial number) then I would file a report, probably not going to get it back, but if the girl does have it, you have proof. If no serial number available, then you can still file a report, but even if she is found with one, there is no proof it is your daughters.
As far as what you should do, be supportive, but let your daughter do the reporting, it is an unfortunate lesson that she needs to learn one day, might as well be now, with you beside her.