If I spellshield Katarina's dagger why does it still drop?

This gives Katarina a means to STILL gapclose to me even though I blocked her spell. I'm not saying she's broken but i'm saying that this is inconsistent to how spell shields work. Someone like Draven's Q is understandably not negated because it is an AA modifier but this is Katarina's bread and butter ability. I guess I should just let her chase me down like a dog?