During the preceding, the Clerk of the House and the Sergeant at Arms of the House were side-by-side. However, during the presentation, the Clerk was next to someone else, seen on the right below. Who is that?
As you and Up-In-Air noted, the Clerk of the House, Cheryl Johnson, is on the left. The woman to her right is the U.S. Senate Secretary for the Majority, Laura Dove.
She is recognized as the Clerk of the House Cheryl Johnson who carried the articles of Impeachment to Senate followed by House Impeachment Managers.