Riven and her e (valor)

So I know Riven had some experimental kit changes with "edge" and all, but the one thing that has always bugged me most about her kit is that low cooldown e. Would a static cooldown be too harsh of a nerf? Late game Riven will be using e to constantly weave in and out of battle but you can't catch her when her e is up every 3.5 seconds. Increasing her e cooldown would allow the shield duration to be increased which I feel would be more satisfying to use. You have all of 1.5 seconds to deal your damage before you become vulnerable again which pushes you towards the assassin play style.

I don't play as Riven often enough because I know she is such a pain to lane against so I ask for some more experienced Riven player to give me a reason not to increase the cooldown of e. I know a static cooldown would reduce he value of building cdr on Riven but would that be a bad thing? Changing her playstyle a bit to more accurately reflect her fighter theme could be better considering that right now all you do is stun Riven and she is so damn squishy she blows up instantly. She seems so feast or famine right now, could a bigger shield on a longer cooldown increase her usefulness to the team? Save the Rivens