If you're talking about full nudity, okay. Otherwise there's more than just 4 seconds.
Hey - Luke Hemsworth needed something to pull in a paycheck between seasons of Westworld. If alien pod people arrived with the master plan of boring humanity to death, this is what might happen. Don't think she was wearing a body suit though. They had her in positions that didn't let you see much, and (I'm pretty sure) used digital masking for the few brief moments when it was needed.
Yeah, there's several detailed interviews about how this movie was done. Every intimate scene used an adult "double" who served as a placeholder. 11 yo Isabelle Nélisse was then digitally spliced into the image. They also gave her non-sexual direction cues. Act like you're running and out of breath, act like bees are stinging your legs, that sort of thing, so they could get the right physical reactions without having to explain in detail what was happening to her character.
It's going to get harder and harder to tell how much of a shot is real and how much is CGI.