Yes it stacks, but only last for the current combat. Meaning after loss/win, her stats go back to normal.
This is a question that I'm still wondering, I know her stats go to normal when the whole battle is over, but does it stack for one round, and end the next, having to stack again, or does it keep going up until the battle is completely over (all rounds done)?
Ok, I may have an answer, I tried sending 9* Vinna to aqua1. As she kept procing their hit rate dropped slowly, and this effect lasted past 1 round. She just kept getting better and better. So, I think as long as she is in one particular battle and say fires for 120 rounds, every proc will continue to stack, it doesn't stop until the overall battle, not the round, ends.
Although, her proc rate would still have to be really good to see a tangible benefit over several rounds.
Pretty tremendous updates online about the games and these are really supportive. The people who really have the skills in gaming and want to improve them can grab help from experts. Thumbs up for your amazing papercheap uk gaming suggestion must visit for more.