This is all speculation. The only thing we know for sure is that her being wronged had nothing to do with Aizen. And no way she was gone for a century, at that time Aizen was still a scrawny Vice Captain, not really the conqueror of HM. Also, Nells attitude in the flashback was that of a loyal model soldier, like Harribel -why would she get pissed at Aizen backstabbing her if she'd always felt he was a total dick? And Starrk joined to get friends.
Also, BANZAI AIZEN SAMA.
The reason I brought up Nells allegiance was that it's something that
should have been made a bigger deal out of and puts the characters allegiance in a totally new light. There was room for some interesting conflict here, but it never amounts to anything because Kubo kicks Nell out the back door after the Nnoitra fight and, as Nobodyman said, just thought up the shole thing on the spot to be Cool.
But you know what, unholy abominations or not, Pesshe and Dondonchakka were still the last two things in this manga I legitimately enjoyed through and through.
I'm not ashamed to say that I find this both decently drawn and funny.
But you know what gets me? A competent author could easily solve the problem of good guys being hollows, and have these characters return - as shinigami. If they really arent ferocious monsters the should have no problem volounteering to be purified, causing loads of souls to move on to SS- including the dominant one that gave them their identity. Then, after joining up with their new allies as ashinigami, soul reaper releases couls invoke their previous hollow selves, but in new interesting ways.
Shame we're stuck with Kubo.