This image only became famous but virtue of the fact that it went viral on twitter and the wider web. If she'd not tweeted it - and as someone with no press contacts - had attempted to sell it directly to media organisations I'm betting she wouldn't have had much success.
I think it's pretty hypocritical to try and leverage free services like twitter for self-promotion and personal brand-building then completely back-track on that ideology and claim some kind of restriction on a particular post cos it suddenly has been delivered to a wider audience and may suddenly have value.