User Accidentally Created Duplicate Calendar

I have a user who wanted to create a secondary calendar for personal appointments.  Rather than create a new calendar, she accidentally created a duplicate calendar of her primary calendar.  Realizing her mistake, she deleted the new calendar.  The problem is that even though she deleted the duplicate, she's still getting duplicate reminders, as if the duplicate still exists.  I can't figure out how to stop the duplicate reminders, since the calendar has already been deleted.