So why doesn't Rek'Sai work mid?

So in norms I have been playing a ton of Rek'Sai mid since I am a mid laner and I got her in ARAM and wanted to try her out in norms since she was fun, and so far across like 15 games the only bad times I have had were against a Annie and a Vex but I also played pretty bad, I get fed almost every game so far and I have never had this much success with anyone else other than Pantheon but he is also very easy, but in concept it seems like she should work pretty well, since she has great roam, decent wave clear, amazing damage, and some sustain. Is it like the same situation as Kindred? where she actually does work mid pretty damn well but nobody plays it?