Buy a shit-ton of armor? She doesn't care. Remember her W's passive? Yeah, sorry. Doesn't matter if you have 400 armor, you're practically paper waiting to be shredded.
Burst her? Well that'd be nice, if she didn't go invisible every second, thanks to her Q's immensely low cooldown. Burst means nothing if she presses R, rolls away, auto's you twice and kills you before you can inhale. Oh, and if a few of your teammates manage to die in the attempt to kill her, sucks for you, she just gained more ult time - and you know what that means? More invisibility.
Duel her? Impossible. Her critical strike makes sure you die in about 3 hits anyways, so either you're also a fed Vayne (fighting fire with fire) or you're dead.
Seriously, how the fuck are you supposed to counter-play this ridiculous, broken pile of shit? Even the highly-praised ADC asshole destroyer, Rammus, doesn't stand a fucking chance against her. I wouldn't be complaining if she took an immense amount of skill, but as it's been said numerous times over, right clicking is definitely not skillful; and for a few right-clicks to single-handedly destroy an entire team is both disgusting and unhealthy.