Only three she can't duel are
,
, and
. The rest, either she can run away from them safely, or win against. I'd say that's pretty good for number of champs one can 1v1 against late game. Ecspecially for an adc, which is pretty darn vital for survival against assassins in teamfights when there's less peel in solo queue. (Note on why Lucian, Vayne, Corki, or Tristana were or are favored at some point in the game, they still could run/ 1v1 assasins)
Master Yi is utterly useless for 1.5 seconds, Rengar is the same thing too, Zed gets kicked in the face when he ults, Kat wastes her jump and her ult everytime she goes in (and facekicked).
(Quinn's an adc for a reason, people. She does pretty decent damage, and can handle most threats pretty well.)