OK, I think of this from the perspective of my 20 yr old self...and then current self.
a) I found the video from We Can't Stop absolutely hilarious. Random, funny stuff. And all stuff that has happened in my younger years at parties (hell, sometimes still happens when drunk enough). It's funny. It's not artistic or interpretive. She's having a good time being silly.
b) At the age of 20, I had been sexually active for 5 years. Yes, 5 years. And so are a lot of people. Why is she not allowed to express that?
c) Her target audience is no longer little kids in the Hanna Montana stage. That fictional character went away awhile ago.
And what's with all the "think of the children" drama? Suddenly our kids are too immature for this content? We've had Madonna rolling around on stage, girls kissing other women AND men during performances, snakes, strip routines, etc... All that was fine. But this...because she's grinding on Robin Thicke (and stuffed animals)...this is over the line?
Really? I think we all need to sit down.
So for my DD, Sally...I'm not explaining anything, actually. She knows Hanna Montana. And that's it. No need to make an association beyond that.