A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
Matsu Otsuko Reaction: After Otsuko or another Deathseeker Personality in her army is destroyed: Reduce the Force of a target Personality or Follower in the current enemy army to 0. Gain 2 Honor.
If she is bowed and then she is destroyed, can she use her reaction?
Matsu Otsuko: If she is bowed and then she is destroyed, can she use her reaction?
Cards out of play are not bowed (http://rules.l5r.com/CE_Physically_mark ... nd_unbowed), so nothing prevents it.