i like it only for a boy. "Dair" souns very masculine to me. I'd go with
Ada,
Adele, or even
Arden (boy's name, but fairly unisex these days - although i prefer that for a boy, too!) for a girl. And I don't think changing the spelling to something else like Adairre or Addayr would make it any better for a girl. I hate it when people do that! sorry. ranting. haha