How can I delete recurring calendar invitations from an inaccessible email account?

Trying to clean up my calendar and I have a handful of recurring calendar invitations that show up on the same day each month. My wife no longer has access to the email account that she set up these invitations from. I have tried every way possible but can only see options to accept, maybe, or decline the events. When I choose decline, the events still show up on my calendar, just with (declined) beside them. Also, when I choose to decline all future events, it does not. It will decline the current month and the next month is still there as an invitation awaiting my response. Please tell me I don't have to live with these forever.

[Re-Titled by Moderator]

Original Title: How can I delete old recurring calendar invitations (from my spouse) that she sent from an email she no longer has access to?