Thats definitely the cause, and I bet you the only way to stop it is to let Yvonne's mother die here so that Elsa wont have to bare the curse, little Elsa of course doesnt know that though, so unless Yvonne comes in clutch (Im guessing the book she picked up last chapter was about the story her mom told Elsa, so she knows of the Sage's curse) to stop Elsa from inhereting the curse, nothing will have changed.