Riot should make it so that if there's a troll on your team, they don't take away LP

Ok. So recently, I played as Olaf jungle and everything was doing good. We got so many kills, and our adc was pretty fed. Then, there came 1 team fight where we didn't do so well, and this pissed off a Fiora on our team. She was mad that we couldn't play as well as a challenger so she started trolling by afking in spawn, and dying to baron on purpose, and this ended up with us losing.

So was it our fault we lost the game? Why should we be punished because a troll lost the game for us? Seriously, riot should really start refunding LP when a troll gets banned.