Against kalista, Extended trades will always favour Kalista thanks to her r. Try and avoid going for extending trades with her.

Kalista’s first power spike is when she picks up her Berserker's Greaves as it will give her the first bit of attack speed she needs to snowball. 

Once Kalista has completed Runaan’s Hurricane, she will pump out a lot more damage and apply Rend r stacks really quickly. Against kalista, The extended trades will always favor Kalista thanks to its r. Try and avoid going to expand the trades with it. Kalista is the first peak of power when she takes her Greaves from Berserker as he will give her the first piece of attack speed that she needs snowball. Once Kalista has finished Hurricane Runaan, she will pump much more damage and apply Rend re stacks really quickly.