Many girls' names nowadays seem to be spelt in any way that fits the sound(s) within it. Consider 'Jacqueline'...that gives us the abbreviated forms Jacqui, Jackie, Jacky, Jackey, Jacki, Jaci, Jacci, Jaki, Jakki and goodness knows what else! So, Charlie, Charley and Charlee are common enough, but why not Charli, Charlii - on the basis of Danii Minogue - Charly etc? Basically, you can spell it any way you like.