User blog comment:IamJakuhoRaikoben/Chapter 461: That Perfume is for Somebody, Review./@comment-5894890-20151109061234/@comment-25111584-20151109120723

lol, Star Dress isn't Lucy's unique skill. It's a CSM Spell. Yukino can learn it too. Any CS Mage can.

CSK just gave Lucy a shortcut to use it before because she was still too ignorant or weak or whatever at that point to have learned it. There is no sacrifice or pain involved in learning Star Dress. Not until Mashima states it in canon, at least.