This is my by far favorite story, and it is such a bliss to see you back in the scene. You have again proven yourself with another great chapter, slowly but yet thoroughly pushing the plot of Sarah.
It is amazing of how you describe feelings and thoughts of Sarah, when she is eventually ending up in the Emilia's shoe. Although the rules of Mother's potty training scheme may be too strict for a teenage girl to bear, it makes Emilia's successful progress of potty training into dramatic turnover in contrast to Sarah's regression. The humiliation that Sarah is feeling makes me really sympathetic for her already, but it looks like this turnover is only yet the beginning. I guess not only the highchair but many other remnants of Emilia's graduation from babyhood (pacifiers and princess pullups maybe?) will be waiting.
Keep up the good work and I can't wait to read the story!