I cant remember the last game where I saw Janna as helpful or important to the game. Most typically it ends with someone playing her that has a higher kill than death count so they think they have done "well".
I don't think you can just change this perception, it falls that way with many champions, most people cant see how weak she is and how little she actually contributes to team fight other than maybe a shield or a heal just to save herself just to run away.
Honestly if I see a teammate try to get her in Aram I just crash the game outright, and if I see her on the opposing team I'm very happy. Havent had her win a game for anyone on the opposite team yet, and you can always count on her to rob the champs that actually needed the cs and kills to be fed.
It is pretty basic stuff but you wont explain it to most of the community, all they see is the kill count, and don't look further into the game.
Best answer, crash if you see her.