She just may put Wigs On Extensions xD
I believe she uses both at the same time =)
Look at the CountDown Live 2004~2005 as an exemple :
1. She has short hair for MY STORY :
2. But during all the CountDown Live 2004~2005, she has long hair :
3. And add to the extension above [^] she used another wig on it :
I think it's the only live where she used BOTH Extension & Wig, because Arena Tour 2003~2004 had just wigs on ourselves and No way to say, the a-Museum for Poker Face's medley and forgiveness, (miss)understood tour for Bold & Delicous, Arena Tour 2002 for Free & Easy and I am..., and finally Dome Tour for SEASONS, A Song for XX & Vogue =)
So yay, at least two wigs for each tour [MY STORY TOUR didn't have any ?? O__o]