Yeah that would be terrible.
It would be as if back in the mage-heavy, projectile-dominated Season 3 mid if they'd suddenly introduced a melee mid with assassin burst damage, a spell shield and infinite dashes who also could block all incoming projectiles.
Or if they had a champion in the long solo toplane who could scale infinitely just by farming one of his abilities over and over.
We all know these broken strategies are uncounterable, too. If such a marksman existed - I'm thinking they might make her a yordle? - we couldn't counterpick even more range-y champs in the botlane
as a counter or anything. Game's just broken, yo.
(I mean, seriously? Pick her or ban her if she's really that hard to deal with.)