Once you reach a certain point with her, she's gonna give you the key for the studio. You will be able to take some pics of her wearing them. You can't make her wear it around the house
When she tells you that, that means you need to progress further with the Main Storyline ( She doesn't have 5 Hearts yet ). She'll change her clothes in the Kitchen when she has Max Hearts, depends on which Route that you want her to be.
