My theory on the breakup
I have a feeling that the fact that Sasha was having such a problem with her costumes was the straw that broke the camel's back and made Sasha leave. In Sasha's journal entries, she talked about her costumes and how Robin's friend was making the costumes for her. Then she expressed frustration about how the costumes weren't ready.
In her Kiss and Cry interview, she said (paraphrasing) how she felt so good to skate in a beautiful new costume. I also noticed that she was really happy skating her SP and she didn't let the mistake get to her.
I don't know Sasha, but I know for myself that everything needs to be right for me to do something. I'm in school and I bring ALL my pens and highlighters to study just b/c if I want to use one kind of instrument and it's not there, then I can't concentrate b/c I keep thinking about how I want to use that item. That's pretty trivial, but Sasha might be the same that she wants to have everything lined up and organized before she can focus. It seems that not only did Sasha have to train between three rinks for ice time (whether this was an issue or not is up for debate) but her costumes weren't ready either. Plus there were issues about the choreography in that Robin wanted to choreograph the programs and Sasha went to someone else. Sasha really strikes me as a very artistic person who views skating as a form of self expression. I kind of got that from her SP. She has always skated freely under Nicks as he allows her to choreograph her own programs. Under TT and RW, Sasha looked really stiff even though TT's choreo is beautiful. Like it or not, Sasha wants to design her own costumes and have input in her choreography. So much has been touted about RW being a psychology major, but you have to adjust your teaching style to your pupil. Robin didn't know when to give up the reins.