To me, the plain reading of that language is that her possession starts on the 6th. I can tell you that my wife and I have the debate about what day "Next Friday" is all the time. She thinks "next" means next week, and "Friday" means the day of the week, so my wife would tell you the answer is the 13th. I think "Next Friday" means the next Friday that appears on the calendar, which is the 6th.
I'd have to see the EXACT language of your decree though. "Following Friday" could mean "Friday following the Friday after school resumes" (e.g. the 13th) or "Friday following the resumption of school" (e.g. the 6th).
Either way, I would not think that either of you could be found in contempt of court and jailed for going one way or the other. According to the wording you've provided, it's an inartfully crafted bit of language.
Good luck!!
