Here is technique available on Youtube and what does not compute with me:

First picture: No support in the lower back.  Not enough leg compression.  A fuller leg compression instantly brings more power (forceXdistance/time).
Second picture: Too much lay back, lower back not supported, because of weak connection through the "shock absorbent knees" which make the draw of the arms inefficient to send the boat or fully accelerate the flywheel.  Such lay back prevents higher effective stroke rates.  I know how to describe exercises that will improve rowing technique and personal performance on the water and on land for this individual.

Xeno Muller, Olympic gold and silver medalist, indoor rowing, rowing technique.