If Anivia attacks a battlefield with Hidden Blade, does Hidden Blade trigger before Anivia's When Attack ability resolves, nullifying it?

Ruling: Yes, if Hidden Blade is played in reaction to Anivia's triggered ability, it will resolve first and nullify Anivia's effect.

Sequence:

• Anivia attacks and triggers her When Attack ability
• Hidden Blade is played in reaction
• Hidden Blade resolves, removing Anivia
• Anivia's When Attack ability fails to resolve because Anivia is gone and the effect doesn't know where "here" is

Nuances:

• This only works if Hidden Blade is played in reaction to the triggered ability, not if it's already on the battlefield before the attack