it should either be "she displaces a greater volume of water proportionately..." or just "greater volume". "Proportionately greater" would imply that the displacement per volume is greater for larger masses which would defy Archimedes Law of Buoyancy. Further, "greater" is a quality, while "larger" is a measurement. For example, one should say "Bucket A is larger than Bucket B" or "Bucket A has a greater volume than Bucket B."
I understand how to play this game.. Ill be back tomorrow to say something stupid..lol