"Edit to add: so my theory is a string of some speculations: Why would Shallan wield the Blade against the fabrial, if not in the fight against her father? - We saw that she is extremely reluctant to get it out. - So from: my assumtion the Soulcaster was broken by the Shardblade, I went to Shallan must have done it -> Shallan must have had the Blade in the fight with her father -> so she must h" . . . .