Jinx is one of the best late game ADC's. I prefer her over Vayne as Jinx has greater range, letting her dish out damage while still being safe. In a teamfight where people are piling on top of each other, Jinx is superior to Vayne as her AoE Q lets her hit multiple targets, getting a lot of people low so she can reset. If the fight is more chaotic and spread out, Vayne is better because she excels at small skirmishes and 1v1. Jinx can do well in a Vayne lane compared to most other ADC's and she scales just as well, which is why she can be played into her. Vayne will beat EVERY ADC in the game if she can stun them into a wall, so as long as you can avoid that, you should be able to fight her as Jinx, though you shouldn't really fight her in a 1v1 if you can help it.