Power Spikes

I don't normally post on here, but this is something that has just destroyed my will to play. 22 minute game of ARAM. For 18 minutes we were doing extremely well, winning most team fights and getting towers as soon as we could. 18 minutes in and we got their nexus down to 25% health. The enemy jinx respawns with a shiny new statikk shiv and black cleaver and continues to destroy our entire team. From previously having a negative score, she then goes 24/6/24 and wins the game single-handedly. Obviously we tried to stop her but with the entire enemy team having cc, it was impossible to get to her. Teams that are clearly winning should not be punished by one person buying a few items. I'm sure this has something to do with the new rune system as well because I am beyond certain that this would not have happened before this pre-season update hit.