Apparently she's a public domain character that was revived by 4Chan as someone who had an extreme and evidently pretty late bloom.
http://the-conservatory.wikia.com/wi...of_Golden_Girl
Here's one with a between panels BE:
the-collection.booru.org/index.php?page=post&s=view&id=19627
I think she's of legal age (depends on the artist) if that's an issue.