It's quite possible to lure the Child slaver out to kill her by bringing Bumble out from the caverns. This does not seem to make other Slavers hostile towards you. You also suffer no Karma loss, since the necklace is never placed on Bumble. "I don't like outside. I'm going home", Bumble will say and return to the caverns.
Killing the Child slaver before luring Bumble or another young child from Little Lamplight will turn all Slavers hostile towards you. Drawing nearby super mutants to her and letting them kill her will not.
Killing the Child slaver after luring Bumble or another young child from Little Lamplight will turn all slavers hostile towards you. Bumble will run back into Little Lamplight and stay there with the slave collar on.
Once Bumble and the Child slaver reach the Child slave house in Paradise Falls, the slaver is disabled and disappears from the game while Bumbles somehow returns to Little lamplight. (She still has the collar on.)