It is in the DLH, on the second floor. You can only book in person, on the day you want the makeover, and I think you book in the DLH store. Not sure about prices - I think they range from about 40e for make-up and hair to about 130e which includes a dress and photos, but don't quote me on that.
There was a thread on this somewhere, but my search isn't working on my phone.
We are hoping to do this on our first day, before we take DD to Auberge!