Nancy, like Elvis, could sing anything and make it all right. It's like certain actors that make an otherwise garbage film compelling just because they're in it. (e.g. Robert DiNiro, Al Pacino, Jack Nicholson, etc.)
I love the idea of an upbeat "Moon River". However, I think this isn't the right arrangement - the thick background texture distracts from the vocals (always the main strength of this song). I think something sparser, with maybe just some bongos or something to keep the beat, would have served this better.