My daughter has crohn's disease. her fecal calprotectin is raised but there are no white cells. dr said this is very unusual. why no cells?

There often aren't: The inflammation in the gut of course involves all three layers of the wall, and white cells are lost into the gut only if there are exuberant ulcers in the inner layer. Ulcerative colitis is more likely to feature a lot of the kind of cells that get into the stool, and I'd draw no conclusions from their absence. Fecal calprotectin itself is just an adjunct -- the best monitor is how she feels.