A bit off topic, but I really hate this whole discussion.
It's a girl sitting down naturally; not a sexually charged pose or explicite act. Literally just sitting down the same way I sit all the time. But because we can see her, suddenly it is sexual, and something to be disgusted or, for some, aroused by. A body can't just be a body. A person (more so women) can't just see their body as their own body, because the second someone sees them it becomes a sexual and taboo object. You end up having to constantly monitor and adjust yourself, adopting other's view of your body as a sexual object to make sure that's not all they see you as. That can't be a healthy way to view ourselves.
It's disgusting that most people's immediate reaction to a naked woman of any age is to see it as a sexual object, painting or otherwise. Not to say I find those people disgusting. It's the way we collectively see the human body, especially women's bodies, that bothers me.
Edit: on topic, how do you actually display or add context to this painting to make it more "appropriate?" We can say add context, but that statement doesn't really mean anything on its own. Most people's issue isn't that they don't know the purpose of the painting (a lot of people can reason it out pretty quickly), but that they were blindsided by something they never wanted to see, or that such a painting existadd is displayed in a relatively public space. Adding a blurb describing the authors intent doesn't rectify that.
It could be moved to a separate location with a warning given before the viewer can see the painting, but I would think that would just result in almost nobody seeing the painting at all. And if so, is it actually wrong to effectively bury artwork like that?
Threads like this, where the conversation become cyclical and gets stuck on a single point are kind of worthless. Once that happens there's nothing left to discussion. It usually just leads to people getting heated and banned over nothing.