Pretty good , but the other karma guide CLEARLY states that karma is best with a melee with a gap closer , and taking 1-2 creeps every minion wave that your carry would've otherwise missed isn't really crippling them in any way.

However , i do prefer solo top with her =)
any tips on countering rumble with her ?

nice variation of karma roles

i play karma alot, as 1stly and support build champ which makes her tanky, played her as ap carry, LOLZ-o-Fun. Often get "I love you karma" from allies and "that sheel" from enemies.
she does indeed do alot of damage and the ap makes kinda tanky as well. for any player that wants to start playing her.. you must must must practice with her.

For me i play her nowadays as a tank. though without blue buff i'm mana starved but still i can tower dive like a bause and walk away "hue hue hue-in" #nobr.

I agree, shes mighty with her damage output, and stacking Ap with her goes well with her passive. Alos you could mention that using shield is better then healing in teamfight ( on y self ofc) because of the Ap boost from passive.

You have a solid grasp on how support and ap carries and are one of the few people on this site that realizes bot lane supports should not farm.