Her mb roll is pretty useless since her forward dash has big recovery and she often gets clipped during the startup. It's still useful in certain MUs like Dr. Fate.
Otherwise, the fact that she is very hard to anti-air helps.
If you are not a patient player, meaning blocking, low blocking, ducking projectiles and waiting for the right moment to strike, you can get easily frustrated playing against zoners with Canary...
I wouldn't necessarily say her MB Roll is useless, but it can be used sparingly with success...
You walk and block. Most people have a pattern when they zone, even the really good players do to some extent, so just try to look for it, make your advance, and get in and go all MKX on their ass.