Though I didn't actually do this to Katie, I've done it to two or three others. This is partly because I LOVE having a well-stocked graveyard in the Sims. At night, they pop out of their graves and roam around. It's awesome. Sometimes I make Sims just to kill them for the ghosts. And if your Sim is enemies with a dead Sim, they get positive mood boosts if they see those particular ghosts (or kick their gravestone). :D Woot.