Did nude pictures?

No. I think you are talking about another person that just looks like her.

There are nude photoshops of her. that's all they are though. photoshops.

There are photos about of some girl that looks like her. But, I doubt that they are of her, they were already in circulation before she even turned 18.

It was some East European model, and was done before Luna was cast. Evanna just happened to bear a striking resemblance to the woman in some of the pics. Oo course, this was when Evanna was 14-15. At 18, she doesn't look like that model, at all, having, um, grown in certain areas. :)

Indeed, that blouse is positively bursting at the seams

She looks like a younger Annaleigh Ashford from Masters of Sex. So maybe you got it wrong.
 to her!