[Gameplay] Sivir can't spell shield Rengar's Q

I've been trying to learn ADC and one of my favorite champions is Sivir. I've been against a couple of really fed rengars who just dive onto me at various points in the game and I immediately throw my spell shield up, expecting the bola snare. These rengars (it was rengar free week) didn't all throw the snare as they jumped in from their ult and many of them used their empowered Q. When they have warriors + ghostblade + tiamat at 20 minutes that Q does about 50% of your health as an adc, and Sivir can't spell shield it.