I do have the exhib perk indeed. I do have an option to access the wardrobe, but the option to access her work outfit isn't there. There's also an option to buy a work uniform, but I didn't find an option to remove pieces of that uniform.
It's not in a wardrobe. You can toggle panties and stockings (separately) in a drop-down menu after pressing arrow up above pound symbol - the one you press to work as a barmaid. Perhaps you don't see it because your character won't agree to work pantyless. If you don't see it try creating new exhibitionist run real quick, I guarantee you there will be an arrow above pound symbol at a bar.