I don't think her progression was unrealistic. For a start, she probably didn't really believe what Brahne said in anger as being genuine. Her loyalty blinded her from reason - until the evidence was undeniable, and that would be expected considering her position.
The reason Garnet's unconciousness caused that effect was because up until then there was always a way (albeit unconvincing) to justify Brahne's actions. But when these actions extended to Garnet - someone who she knew, it become patent that her reasons for genocide were pure fabrications. She knew first hand of the innocence of Garnet, and so the actions taken against her could only be condemned.The fact that seeing Garnet unconscious somehow made her suddenly think: "genocide is bad" is also...bleh.





