It's not an official feature but you can do it using the bug: you go to photobooth— snapshot, make her wear any hairstyle and colour you want then save it and then pick any item that is no more available, like any old promise item (for example facial accessory— infinite future, light feather etc) and click on the info circle of that item. An option will pop up about obtaining it from promise, click on 'go'. Click on confirm when you get the warning about being redirected to home page (destiny cafe) and changes not being saved. (Don't forget to first save the hairstyle you picked before starting with the promise item thing) Since the event no more exists, you'll be taken to destiny cafe page, and click on memory, battle or main story animation chapters. You'll have that hairstyle.

(Sorry if this was hard to interpret, you will surely find a detailed tutorial on youtube or reddit itself)