I honestly don't know what picture you're referring too, 'cause all of the pics I've seen in this Post are strictly non-nude. However, assuming whatever you are referring to is correct, then what you are referring to -- both morally & legally -- is an invasion of one's privacy, and if that were true, if she -- or in her case, since she's not of legal age of consent to such private material, whether she took a photo of herself or not, then her parents or legal guardian(s) -- has a problem with that, then they can seek legal counsel --- like anyone (example: JLaw & Kate Upton did with their lawyers)--- to bring those said image(s) from being shown, viewed, seen, &/or displayed online. In short: If they have a problem with any of it, then they'll take (legal) action. If not, then either they don't care, or the pics aren't real/legit. So if they don't have a problem, then why should you?
FYI: Even if it's real, whatever picture you're referring to, these sort of online nudes of underage celebs is nothing new, example: Natalie Portman, at the age of 12, went sunbathing nude on some nude European beach, and candid photos of her underage naked body not only surfaced online, but were actually splashed onto millions of newspapers and magazines around the world, and -- while she wasn't too happy about it -- nobody really gave a shit, morally or legally, and she still went on to become a great, talented, world-famous actress.