Calendar: Remove old invitee addresses

My wife recently got a new business email address. I've removed all instances of her old address (I get nothing when I search my iMac, iPad, or iPhone), but it still appears as an option when I invite her to events. Unfortunately the old address is very similar to her new one and I have occasionally sent the event request to the wrong place. Is there any way I can permanently delete the old email address?

This is only an issue within Calendar, none of the other applications (Mail, Messages, FaceTime) are a problem.

Thanks in advance!

David