WW doesn't always nail it exactly. Sometimes you need to tweak a little with a PBM or the Morph Brush, and then create a new Anastasia FBM (in Poser, not WW) with the tweak included.

In this case it's a little loose on the hips, so if there's no Hip Size morph in the reborn pants, I'd use the Morph Brush to work around the upper edge of the pants and make the waistline a little more snug. As for the jaggy area at the thigh joints, that should be fixable by smoothing with the Morph Brush.