Her kit works well as it is, but then there's overbearing parts of abilities that probably need to be addressed.
**What I Expect Riot to change (Something along the lines of these.):**
1. Put a damage cap on her Rend vs. Monsters for the sake of Dragon's and Barons getting nuked for 1k+ HP.
2. Remove/Reduce Mana Return on Rend.
3. Remove/Reduce Application of Rend stacks on multiple targets via Runaan's Hurricane. E.g. Kalista AA = 1 Stack, Runaan's Hurricane Bolt = 1/2 Stack. This would slow her wave clear but still keep it relatively intact. It would also put more emphasis on Kalista focusing targets rather than just spamming auto attacks and Rend'ing anyone that's marked.
EDIT: 4. Reduce Kalista's Attack Speed per level by ~0.5.