LOL, for one dude, if she hits a vital when chasing as long as you're in front of her shes not going to be able to keep getting proc's, you know why? because they rotate to never spawn in the same side twice. Two her passive is her main damage output, of course its going to hit for a significant amount, but still it'll take upwards of 7 passive proc's with that damage plus she has to navigate around your champion.
And two, she is not broken. her early game is awful, she lacks team fight prowess and takes quite a bit to scale up. She cant contribute much to a team fight, she splits, and is a great duelist, so don't try to duel her. Almost no champ can out duel her, so bring friends, because she trades her team fight presence for her dueling prowess. Here's why shes balanced. Her W is a massive cd with with a very very brief active, so if W gets messed up her dueling ability gets diminished greatly. Her E is a shadow of what it used to be. her ult is countered by standing next to a wall, same with her passive and her Q's travel time gets reduced by slows, did you know that? probably not.
Here's what you do in lane. Set her behind get jungle presence, bully her, her early game is shit, take advantage of that. Get your jungler to gank her, shes susceptible to ganks, because even if she tries to Q out the cool down early is just too high. If shes splitting 2v1, that's how you counter duelists, or team fight, wipe out her team with your 5v4. When fighting her 1v1, 2v1, 3v1 it doesn't matter, slows hurt her a lot as it affects her Q how fast she can activate her passive/R. Get a Randuins, the crit reduction reduces her E's crit and the attack speed hurts her dps. The slow makes it harder for her to get to her passive, because like i said, even with using her Q it still slows its travel time. She doesn't have the CC to lock you down, her E slow is only 30% at all ranks and her W's cd is too high to matter, especially if she wiffs it.