You know..... If powder wanted to send a message (and there was a write in) I'd suggest letting her live... Bit crippling her in a way that would send a message.
For example.... A nail to the spine could, quite easily, leave her paralyzed.
Pair of nails to her eyes.... Blinded.
A nail to the Achilles.... Good luck walking.
If we COULD I'd love to leave her nailed to a wall and a nice little scene spay painted around her.... Specifically Silco poisoning our father and sending him to the bridge, ending with him shielding Powder.
I doubt we have time but swinging by Zaun to leave behind Graffiti of what REALLY happened, possibly with names of those who died to Silco would be really fitting.... Bonus if we include powder in there.
If we did a verbal message I would suggest "You killed the Hound and his pups.... And let Jinx out to play. -Jinx" or "What do you call someone who kills their friends? Jinxed."
Not saying we should but I would love the scene of her nailed to the wall, alive, and possibly it serving as the start to the Firelights. Heh, can't get the idea of the Firelights possibly having a different name in this timeline. The Jinxed, The Pack, Hounds, or more....