When you import the green screen girl, you need to place her on the left side of the first girl, not directly on top of her. You then move the GS girl to the left after she has drifted up, but that doesn't give the Motion Tracker tool any clue as to how to connect those two different locations.

So start over, and place the GS girl on the left in the first frame. Next, as the tool previews the motion, stop it and manually make any adjustments needed to GS girl's location before continuing the preview. That way, the MT tool can adjust its path by integrating your manual placements and it should give you better results.