Save a disable (stun/snare/silence/knock-up/displacement) for her to stop her from channeling her ultimate and dealing massive AOE damage.
Katarina is weak at farming under tower at earlier levels, so try to pick something that pushes hard.
Zhonya’s Hourglass active, can counter Katarina’s Ultimate.
Buying a Guardian Angel will revive you after death denying the resets Katarina would have received from her passive.
When in lane, stand apart from your minions. This will stop the bouncing blades from hitting you. She will have to make a choice to throw the blades at the minions or at you. If she throws them at the minions, then engage. If not, then just farm.