Rules FAQ
- If Alys is already standing (or if she cannot stand for some reason), she is not a valid target for Sigorn's ability. You have to stand her successfully if you want the post-then aspect of the effect to resolve.
Lord. Wildling.
Reaction: After you win a challenge in which Sigorn is attacking, choose and stand another Wildling character you control. Then, if that character was Alys Karstark, stand Sigorn.
Link: Decklists
Rules FAQ