Using Classic Outlook on Windows for personal email, calendar, and contact management
Thank you for letting me know.
Since this was working before and your wife's access suddenly disappeared, can you confirm whether the shared calendar has completely disappeared from her Outlook, or is it still listed but no events are showing?
Also, is your wife using a Microsoft personal account (Outlook.com, Hotmail.com, Live.com)?
As a first step, try removing your wife's sharing permission from the calendar, save the change, then share the calendar with her again and have her accept the new invitation.
Please let me know what happens after re-sharing and whether any error messages appear.