I'm listening to Ogerpon's theme... she holds the memory of her partner in every battle she fights... it creates a warmth in her heart that lends itself even to her most selfish and greedy enemies...
I think she would spare Pecharunt, even after everything it did. And not in like a 'killing you would make me just as bad as you' way
But rather in a 'I am at peace with my past and even though you may deserve death, there's a stubbornness within me that pushes me to make you realize the error of your ways, and fight for your self-improvement despite the guilt' way