It probably isn't necessary to wear Le Chateau, but wear something of a similar vibe. Dress like the employees dress (particularly like management, who tend to follow dress codes more carefully), but maybe even a step more conservative and nicer. I don't know what kind of store Le Chateau is, but generally I wouldn't advise wearing lulu lemon pants OR leggings--both seem too casual for an interview. Wear actual pants, or even a skirt as long as it covers your thighs when you sit. If the store sells nicer clothes, you might wear a suit--or at least long sleeves. If it pretty much sells cheap-o trend-of-the-moment clothes popular with pre-teens and teenagers, you can get away with being a little trendier in how you dress for the interview, but don't wear jeans or sneakers or anything like that.