There's a level of power among only a few of the top players:
Serena, Clijsters, Henin-Hardenne, Lindsay, Venus, and Capriati
These are the only players who hit consistently with aggressive power, however, of these players, if we factor in movement, shot selection, and the ability to construct points playing defense and offense, the list is whittled down to:
Serena, Henin-Hardenne and Venus. These are the three players that Kim has the most trouble with. With Lindsay she simply retrieves all the power until she gets a wide-open court to hit into, and the point is over. With Jen, Kim does much the same, only she can rely on Jen not being the best thinker out there, and almost always centering the ball, and then making the unforced error after the ball is in play longer than 5 or 6 strokes.