No edit button on calendar events

You have two or more accounts and have send yourself event invitation. Account you are checkin the event on isn’t the event owner. That is why you can delete but not edit the event.

Other option is that the account is configured in a way you can view but not edit events.

That isn’t an event you own. It’s an event owned by Jaclyn who invited you to it to join. It was shared to you from other account.