It's possible to prefer dark tones and jewel colors without sporting a languid and mysterious affect. Black is, after all, slimming. This should help you explain your actions if your tween suddenly recoils in fear because she suspects mom is going goth.
Still, if you're slipping into your tween's makeup bag to borrow her black nail polish and eggplant-hued lipstick, there's a problem afoot. Goth, in all its drama-inducing glory, is for the young -- not the young at heart. So let your tween outfit her personality in lace-up boots a la "Clockwork Orange" and pair them with long black skirts and lacy tees. As for you, momma, let your goth flag fly by layering a black lace shirt under your blouse or buying a velvet skirt.