Outlook calendar. How do I delete it?

I imported another user's calendar as a .pst to check it. It is now the default calendar in my account. My actual calendar became a secondary one. My calendar was blank anyway so I don't care about losing it I just don't want her calendar. It's flooding me with to do list items. I cannot figure out how to get rid of her calendar out of my outlook.  It says it is my default calendar and cannot be removed. It was NOT my default calendar. It needs to go away.