Fibers are selected and blended in certain proportions so the fabric will retain the best characteristics of each fiber. In some blends the polyester even makes the fabric machine washable. Variations in the hand and appearance of fabrics with the same fiber content can be caused by differences in the weave or finish used in each fabric. The use of textured yarns, a modification done to many fibers, prior to knitting or weaving, can also alter the appearance of a fiber from smooth, lustrous, and flat to crimped, dull, and soft. I agree it's undesirable to have to dry clean your daughter's clothes.
Polyester is washable.
However, if the label says dry clean only there may be a linig, collar, trim, embroidery or other embellishment which shouldn't be washed. It's there for a reason. I have a long dress of rayon velvet that fell on the floor on the bottom of closet and is wrinkled. Velvet, particularly high pile velvet, can not be pressed flat with an iron, because you will flatten out the pile. These can be purchased at most large fabric centers.