Being "void" inside, or feeling void, is different conceptually from the Void, and while i agree the looks fits well with the rugged stuff and all still my point stands: she does not stand thematically.
I agree that she could have journeyed to the void and got powers and such, but at this point every champion, no every subject could do that and be worthy of a void skin; If you really have to think about a skin then better pick up the most worthy ones, the ones that does not only give cool ideas but also thematical cohesion.
An eventual Fullmetal Riven for example would give thematical cohesion, since she was a soldier.
Another cool skin Void related idea could be Void Zac, that not only needs skins but also can feature the concept of self-consuption. Or Nunu.
However each one has his own opinions, and we both agree that is still cool as heck don' t we? ;D