It's not clear if she'll get a new outfit but the one on the cover could be solely for the story.
I'm going to be honest, I never saw the appeal of the character. I never hated Harley but I never got the hype. It might have to do with her going back to Joker all the time. It seems impossible to be her own woman when the writers will keep bringing her back to the same abusive relationship.
Great news for her fans and at least there's a good team on the book. In the meantime I'll be keeping my fingers crossed for a time travel book.