[@Cojemo]: I still feel like it should be a bit more, say... maybe the dance has a compulsion effect that makes you watch it unless you have good enough MR or willpower-related skills? Or maybe the dance and the attack are a single effect, so if you look while she's dancing a curse is inflicted that opens a hole in your chest and kills you?

I'd try and use other conditional kill NPs as a model, like Maria the Ripper for example.