I can totally imagine that she's been trying to get a twitter forever and possibly was part of the drive to let ANGERME use one every once and a while and now that she has more power over her own media presentation it's the first thing she does .
I could totally see her doing her own vlogs on youtube too, she has such a internet star quality about her in that she wants to produce herself and have that control over what it is because she's doing it all by herself.