Stormrazor unique passive completely non-functional on Ashe.
Outside of actually forcing the attack to be a crit to trigger any crit related effects Storm's Edge has no damage effect on Ashe due to being overridden by her passive.
While I do agree that this seems to be game mechanics working as intended and potentially not really a bug. I do think that forcing it to override her passive in cases where Storm's Edge would do more damage than a passive based crit or even in cases where the target is not chilled would make more sense (and would stop the item from being dead on her, although would still be an unlikely item choice).