Question about Kalista's Pierce, idea for buff to her

I have a question about Kalista's Q ability, pierce. I think I know the answer, and if so then I have an idea for a good buff to her without strengthening the toxic aspects of her kit.

Does pierce provide a stack of rend on 1-shot kills? Such as: if the enemy adc is behind a caster minion (full health), and I toss a Q through the minion and hit the champion behind, will the champion have 2 stacks of rend (pierce hit on caster + pierce hit on champ), or just one stack?

If pierce doesn't currently pass the stack it grants through to enemies when it slays one, maybe it would be a good buff to give it the benefit of providing its own stacks?