[name]Sunday[/name]? Is that the only name that [name]Sunny[/name] is a nickname for? Nameberry’s blurb on it says that it’s too nick-namey but fails to say for what.
I think it would work for anything with “son” or “sun” or those letters spread apart in it. Examples: [name]Sonia[/name], [name]Alison[/name], [name]Susannah[/name]
My first thought is summer. Or it’s just a cutesy nickname unrelated to a girls name. I think what NB meant was that it sounds like a nickname. Not that it was a nickname for anything 
I know two girls named [name]Sunny[/name] and it is actually their name. [name]One[/name] is in her teens and one is 3 years old. I think [name]Sunny[/name] is great on it’s own! [name]Sunshine[/name] is also very today.
[name]Simone[/name]
[name]Sandra[/name]
[name]Alexandra[/name]
[name]Santana[/name]
[name]Sarah[/name]
[name]Soleil[/name]
[name]Marigold[/name]
[name]Golda[/name]
[name]Sunshine[/name]
Any girl with a sunny disposition I suppose.
I love [name]Sunny[/name] on a girl.
Sunniva, [name]Sundance[/name], [name]Santana[/name], [name]Sidonie[/name], [name]Sullivan[/name], [name]Serena[/name], [name]Sonnet[/name], [name]Sonora[/name]
I think it’s most common for [name]Susannah[/name] or Sunniva.
[name]Susannah[/name] was my first thought, but my favorite is Sundara/Sundari it has a lovely rhythm and it means beautiful…
I knew a girl named [name]Sunny[/name] growing up and that was her full name. Her last name started with an “s” and her name was peppy and memorable. I’d never name a daughter [name]Sunny[/name] but it worked for her.
I taught a little girl called [name]Sonnet[/name] once, and we called her [name]Sunny[/name]. Also I have always loved the name Sunniva (already mentioned here) which has a wonderful meaning.
When I went to High school, there was a girl named [name]Sunny[/name]. And that was her full first name.