We have 11 y.o. twin girls who share a room. In the last 2 months, one child completely melts-down when her sister sings, hums, or whistles. Yelling and shouting, she demands her sister stop immediately. We've told "the yeller" to remove herself to another part of the home, use ear plugs or choose another coping skill. No such luck. She insists her singing sister is the problem, not her. When sent to her room to have a "private melt-down moment", she is destructive w/her sister's items. What course of action do you recommend we take?