it is true, marjolein does look very muscular...i personally think she has gone a bit too far, although i think her look is v popular in the us (sarah jessica parker, madonna and others have that same look). that said, she looks a hell of a lot better than me, so i should not really comment!
i think if anyone does want to acheive the same look though that it is possible through pilates, although as misstibbs says, 20 mins is not enough to make it happen - i used to go to a spin class and had an excellent instructor who had the same look. i asked her what she did and she said apart from spinning, she did masses of yoga. most of the other women who had the same look did weights classes, but she must have done probably a couple of hours of yoga and spinning a day, so pilates can work, if you do enough and maintain it with a good cardio workout also.