In the scenario described, Lexi folds the paper so that point C is on top of point D, which means the fold creates a line that is the perpendicular bisector of the line segment CD. The intersection of the fold with the line segment is labeled as point E.
Since she draws lines CR and DR through points C and D, respectively, and both extend through point R, the segment bisector of CD would be the line that bisects the segment perpendicularly, which is the line where the fold occurred.
Therefore, the segment bisector in this scenario is the fold line that goes through point E, which is positioned such that it divides the segment CD into two equal parts at a right angle.