29th May 2016: Alterations are go... I put in a new stronger zip today and thankfully that did the trick and it fits great now! I let it out a little at the waist and it fits a lot better too now - thankfully where I let it out is where all the gathers are anyway so it's not noticable. I also ordered a tiara for her off ebay - I was going to mod one I had but found one that I thought was pretty although not completely accurate.
Will get around to sorting out the rest of the accessories at some point - not a lot to do thankfully, just securing bits here and there!