It was a sci fi book, with a redheaded girl on the cover in this gold like, dress or suit or something, she was kind of at the bottom left corner and there was a planet/moon/celestial body behind her? I think?
Details I remember vaguely: she was sixteen years old (but she was on another planet so she aged differently), there were either two moons or two suns or possibly both, she had this singing dress that her caretaker made her for her birthday, she and her caretaker were the only people on the planet until this group of humans arrived and then she fell in love with one of them (I think his name was Michael?), she found out that the caretaker guy had altered her body so she could live on the planet they were on?
I've been Googling all night with various permutations of the above keywords ("singing dress two suns Michael" for instance), I've combed through all the pages at TVTropes that looked like they related and I've even read through the bibliographies of several sci-fi authors that I know I've read / could have written it. I can't find anything. Please help?