Responses
It's not to "restore world balance". She swapped in the first place because she envied her friend Beatrice's life. Then, when she saw that her old body is doing well in life (the duke is head over heels with the current Realiana, the high priest and the emperor are in great terms with her, etc.), the soul of the old Realiana is now envious with the current Realiana, so she wanted her old body back or at least kill her to live the life the current Realiana has or something because she thinks the current Realiana doesn't deserve that life. So, it's greed not world balance.
Beatrice is the real Raeliana. I think Beatrice did something to swap their souls. Now "Beatrice" wants to kill "Raeliana" to restore world balance.