What kind of box? A simple rectangle, or a 3D/2D thingie looking like a box? What happens then? Or what happens not? How exactly is she selecting, copying, and pasting? When is she copying, in relation to creating the box? Why is she copying a box? Has she only tried with a box? Has she tried copying to a new Illy file, or to a new layer? Version of Illy?
What do you mean by copy or paste, or is it copy and paste?
Try moving the whole folder containing the AIPrefs file to the Desktop while Illy is closed; this will recreate faultless defaults.
It is a hidden folder. Up to 10 it is called ...\Illustrator 10/9/whatever versions. In CS it is called ...\Illustrator CS Settings, in CS2 it is called ...\Illustrator CS2 Settings.
If there are more users, each has her own so you have to look for the user name in the path.