I'm assuming this thread is in reference to Elana the Squallid Queen. While everything I'm gonna say is just speculation, and I myself can't think of any way to bwack it up, it is likely that since they are sisters they shared a lust for power, and awoke Sinh so that he would take down the Sunken King and she would have power, like how Nashandra caused the war with the giants so that she could take power from Vendrick. Just my idea.