What are some fun things to do in DC with my 7 year old niece?

I’m meeting my sis and my niece in DC for a week this summer and would like some ideas for things to do that are NOT educational. We’ve got the Zoo and several parts of the Smithsonian planned. She has been dragged along to every “science-y” museum in the country at her brother’s wishes, so this time I’d like to gear the activities toward a very “girlie girl”. Where do 7 year old girls like to shop in DC?