I beat a riven In lane.
I still think she's grossly over tooled. Her AA cancellation allows for insane burst, And her Low CD mobility compounded with her stun/knock up allowed her to poke me down, before I could retaliate until she could all in. All in all, I don't see a real weakness with her. Her squishiness is covered by her Shield, and she's incredibly slippery. Even Nasus, with his Banana's late game potential, still has to put his team into a 4v5 and has to farm before he can reach that point. (And I hate playing against Nasus more than I hate playing against Riven, if that says anything) It's not that any one element that makes her stupidly strong. It's that her entire kit has so much synergy with itself. (Building CDR+ Resourceless, Or AOE Stuns/knockUP+ AOE abilities, HighCD + Mobility etc.)
Honestly, I'm not sure what Riven would need to have done with her to balance her out, but she definitely doesn't seem fair as is.