Full Access permission user not able to delete item within a calendar list

Issue is occurring with a single calendar with multiple (9) calendar colour coded views.

The issue is that a user (with full control) has been receiving error messages when they try to delete a single entry from this SharePoint Calendar. The user however does not experience problems when they create and/or delete the entire list/calendar.

Error message looks like: Sorry, something went wrong The User [user] is not permitted to perform the deletion of Item [List].

We have two full control users, would this be an issue?

We have tried removing/re-adding her, with different permission levels with no luck.