"Did you get all that information about the wand, Elliot? I hope you did, because it's all very relevant to the current situation, and will undoubtedly remain so for quite some times."
Nanase's hair grew extra long as a side effect of still recovering magic while burnt out. When Nanase used a magic watch to try to control her hair length, it started growing uncontrollably, then stopped (right after being cut off, whoops). After that, the cut hair went "poof" in a burst of magic, making Nanase and Sarah's hair grow (Tedd resisted this magic because of seer-related nonsense).
Tedd has a LOT of notes on that incident, but not a lot of conclusions.