Every 20 seconds? Didn't know you could have 60%+ cooldown reduction.
In any case, Katarina (not Katrina) is a lot like other assassins - if they feed early on, they will dominate the game. Otherwise, they can easily find themselves struggling to be useful. Katarina specifically has no CCs of any kind, and relies almost entirely on Death Lotus to be useful in group engagements. All it takes is one stun, knockback, fear, silence or grab to render her very weak for the next 60 seconds. And that's ignoring the inherent issues with a melee character with low health and no disables.
Finally, a big factor in making Katarina seem absurd is her passive - an assist/kill reduces all cooldowns by 20 seconds. If you're losing badly, that passive will let her use Death Lotus twice in one fight. Otherwise, it will have significantly weaker effect.