Peculiar game: Who would you report here if any?

So, Riven and Sona were carrying our Ranked Game. Then Sona misplayed one situation, which caused Riven to vent: Riven called Sona "useless" or something the like. Because of this, Sona decided to not participate in the game anymore: She didn't _feed_ outright, but she didn't do a single point of damage from then on either. Sona - in her own words - wanted to teach Riven that no teammate is ever truly "useless" - as long as they aren't trolling. She turned out to be right: Without Sona, we lost that game. Riven - seeing the almost certain win slowly escaping her grasp - started to flame harder: She called Sona "r%%%%%ed", "degenerate", "jew", "jehovahs witness" and wished Sona's mother to die, amongst others. In the end however, she came around and agreed to talk this out after the game -- sadly too late, we had been way outscaled by that point. Now the thing is: In that talk in the post-game-lobby, Riven kinda agreed to not flame a teammate that is not trolling nor feeding in future games. Probably more out of fear that she might lose a game in this manner again than anything else - but still. I'm kinda conflicted here: Who did what wrong? Who is to be reported for what? What's you guys' opinion on this?
Report as:
Offensive Spam Harassment Incorrect Board