If it's a skirt (i.e. extends no higher than the figure's waist) then you probably need to add some constrained vertices at the waistband as infinity10 says. If it's a gown (covers the figure's shoulders) then try the same thing at the shoulders. Make sure you have enough of the figure in the collision list, of course. :) Could you post a link to the outfit's product page so we can see what it looks like? By the way: absolutely DO NOT Google for "Angels for Young Teens" if you value your job and/or marriage. :D