Rules FAQ
- Arianne Martell can trigger her ability when a duplicate comes out of shadows under your control.
 - If playing an event from shadows is the triggering condition, the effects of the event resolve first before you trigger her reaction.
 
Lady.
Shadow (5). Stealth.
Reaction: After a card comes out of shadows under your control, choose a character. Until the end of the phase, that character loses a challenge icon of your choice. (Limit 3 times per round.)
Link: Decklists
                                                    Rules FAQ