“they were within their rights to reverse an admissions decision.”
I will leave the discussion of whether it is or isnt within their right to reverse their acceptance decision to others.
This is directed at the alleged actions of the school, where they notified the family of the change by informing the girl in school, on the first day of school. it would have been hard enough on her had they called the house the night before, spoken to the parents who would have had the difficult task of breaking the news to their daughter, but they would have done so with compassion, let her cry our her frustration etc… but, to inform the girl, in school a mistake was made and send her home?