I must say, that Sarah arc is intriguing. We could see, that she seems to get a lesson from the whole Eris affair, but, her old nature is still boiling inside her and probably will be for a long time. She seems to be able for some act of kindness towards Sonya but otherwise, her world view is stil strongly paired with her sense of superiority. To some extend she may have arguments for that - comparing her for example with Yuki (she is intelligent and has knowledge, while Yuki lacks of it, although not that much because it is her fault), Alice (I think she desipses her too deeply pushed humility as something like 'asking for forgiveness for the sole fact, that you are alive') or even her own sister (similar issue as with Alice, yet not that much intensive).
I'm looking forward to see more about her journey to the position when she could be ordering and executing punishment of herself, as it may be good story of other characters (who will not be so eager to give her that position, for good reasons) and herself (we will see, if she will be able to resist the temptation of overusing this power over others).
Also, we do not known her talent yet - maybe it will not be something big and shiny, compared for example to Sonya or Yuki and she will have to swallow it somehow (or maybe she will be doing heavy thinking on how to put her weaker talent to use in unorthodox way, to show it is actually stronger, than everyone else are thinking?). But it may be also something strong and it will only reinforce her balancing on the thin line between her good and bad side?
In general, Sarah is very interesting character, because she is complicated and has a 'dark side' that she needs to work on, but that also is part of her nature, so she cannot fully reject it 'just like that'. I think that makes her different from other girls, who, in general, does not have a 'dark side', maybe aside of Hazel, who was a bit jealeous - but overall, she is a positive character.