Spoiler I touched on this in a earlier reply but there was no "snapping out" of those delusions since she firmly believed she deserved everything Senianna had. In the final ark where Sharlina is stabbed (sacrifice I think?) and Senianna almost being turned into a puppet by the priest, the building they are in starts to collapse. Sharlina pretty much begs for Senianna to save her but Senianna reminds her that when they were kidnapped the first time thanks to said delusions, that Sharlina just watched without helping. Senianna did the same and it is assumed that Sharlina is crushed to death by the ruble. This is based off memory and I read this a while ago so I could be a little off
Can anyone share the brother's and grandpa's reaction when they found out the truth about the current sienna being the real one and that there was a fake?