User blog comment:Xilinoc/Ch. 569 (You've been hit by / You've been struck by / Senbonzakura~)/@comment-7079377-20140221113541/@comment-11051098-20140221211409

We don't really know anything about her progress during the 17 month time-skip, other than being promoted to lieutenant.

The RG training have obviously increased her power and maybe some abilities, but it is possible (as someone else proposed) that she learned Bankai during those 17 months. She could have achieved it then, but only become strong enough to use its abilities during the training she got from Ichibei.

Something. Kinda. I don't know.