Calendar and Outlook have unexpectedly synced

We have a shared calendar accessed using the native Calendar application, as well as a separate Exchange environment. Yesterday, for one user, the entire contents of the shared Calendar imported into her Outlook (2011). I can't seem to find any indication on why this happened or how to reverse it. It has since replicated to other devices that she connects to Exchange with, as well as Outlook Web App. There are two devices that have both accounts on them, a MacBook Pro OS X 10.8.4, and an iPad. The iPad Exchange account was not set to sync the calendar. Nothing is checked under Sync Settings on the MacBook. It seems to be a one way import only. Any thoughts?

Thanks-