> Antonia Colins, who runs the website Balance Through Simplicity, has two adolescent daughters, one of whom struggles with neatness

Another possibility: the daughter is at ease in both neat and messy environments, but the mother is only at ease in neat ones. In this case, the conflict is being driven by the mother's struggles - not the daughter's.

Taking the unmarried marriage therapists advice and escalating your nagging to email is a disaster idea. You can't performance manage a relationship. Nagging and trying to change people doesn't work. Communicating your needs and reaching compromise does.