objectively I would not see much wrong with it, although I would have discouraged my kids from wearing it, but you are the father and if you object, that is the end of the discussion, she does not wear it. However, I would not come in and start yelling at the child to take it off, since the wife has just bought it. I would first sit down in private with my wife and discuss the matter, since obviously we are not in agreement on a relatively simple issue. Then I would explain quietly and simply, in one sentence, why I find the costume objectionable and invite her to come with me while we exchange it for something suitable.