Murder in Dungeon World

I have a female fighter (level 3) just starting a personal quest to find her ‘missing’ twin sister.

For the whole game to evolve it has to start with her openly committing murder in a crowded Tavern.

She will do this by guile and subterfuge, playing on her beauty and apparent innocence, to obscure her real motive when approaching the un-armoured male victim – who is with a number of his associates – she declares that she wants to use her good looks and Charisma to fool the victim into thinking he has made a ‘score’. She will get close up and almost personal inviting an embrace from him at which time she guts him from crotch to sternum (with all the gory steaming details) with a concealed blade.

So how do I run this? She is not into a ‘hack and slash’ move, so should I use ‘deal damage’ with a + modifier, or simply take the murder as done and simply describe the ensuing scene and ask, ‘what happens next/what do you do next’?

I’m asking as a player and as a GM. I play solo most of the time, but sometimes also with a small group as either a player or a GM.