What Should My Wife Wear to Her Interview?

My wife works in a museum as a child educator. The dress code there is very casual (she has always worn jeans and sneakers, as does her supervisor). She is getting a promotion, but she still has to go through the whole job hiring process, including an interview next week. The interview is in the middle of her work day. She's not sure how to prepare for the interview as far as her outfit is concerned. The people at her work have never seen her in anything but jeans. Is it ok for her to do the interview in her typical clothes, or should she wear something different that day? And if so, what would be an appropriate attire given the current dress code?

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