To unlock the Boutique key, complete the game (on any difficulty) and choose to save over your game once you have done so. Start a new game on the save file and Jill will have the Boutique key. Enter the Boutique that is located in the Uptown area. Jill will be able to change her outfit from a variety of outfits. You can unlock more outfits by getting better ranks on each difficulty. To unlock all of them, just get an A rank on the Hard difficulty.
Keep in mind that you can return here anytime during the first half of the game to change your outfit. However, once you board the Tram in the Downtown area and leave the Downtown, you can no longer return to the Boutique to change your outfit.
Added by: Volke Apr 27th 2009, ID#888