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.
"Reaction: After Hisako is destroyed: Dishonor another target Personality who opposed her when she was destroyed, or who performed the action that destroyed her. The target cannot be rehonored this turn. Bow him if he is Crab Clan."
Should this be taken as "An army that destroys Hisako during battle resolution gains no honor for this battle" or does one gain honor following her Reaction going off?
"Reaction: After Hisako is destroyed: Dishonor another target Personality who opposed her when she was destroyed, or who performed the action that destroyed her. The target cannot be rehonored this turn. Bow him if he is Crab Clan."
Should this be taken as "An army that destroys Hisako during battle resolution gains no honor for this battle" or does one gain honor following her Reaction going off?
If there is a clear winner and loser in a Battle Resolution, then yes, Hisako's death and subsequent Reaction will happen before any restoration to honor or honor gains from Battle Resolution. That means you can prevent prospective Honor Gains for a victorious Attacking or Defending army that ran over Hisako.
However, in the case of a Tie restoration to Honorable Status happens before armies are destroyed (thereby ensuring everyone dies as Honorably in battle). In that situation Hisako's reaction won't prevent any Honor gains.
For more information, check out the Battle Resolution entry in the L5R Comprehensive Rules