I believe she went public because she is a writer who lives much of her life in the public eye. I could be wrong but I think that many of her articles give details on her life - so this is just one more detail that she has revealed to the public...
But I could be wrong about that. I've found her archive at
http://www.jilliannyc.com/clips.html and most of those stories don't seem to be about her... But the "coming out" story is the only one that she has had published in the New York Times. Maybe that was part of her motivate - writing an article that was so powerful that it would be accepted by the New York Times.
Regardless, this has me thinking of the "it gets better" campaign. I'd love to see a series of successful (or even relatively average) people coming out and saying "Yes, I'm into spanking. It's something I enjoy and shouldn't looked at as weird.".
Goodgulf
(who uses a fake name when he posts about spanking, a different fake name on a fan fic site, a third fake name on a political site, and various internet handles)