Find me a Jane off the street who *wouldn't* have relatively childish body language in that situation
I think, given the circumstances (and to add to it, Adam's phrasing suggests he feels there's something wrong with Renee and the girl having sex, period - what that is, there's no real indication, I can think of at least 3 valid explanations*), it's a miracle her body language isn't more 'childish' - under these circumstances, I'd not be surprised to see someone lead out of the room in tears - especially a young person.
* She could be underage - at at least too young for Renee in Adam's mind; Adam could be a homophobe; it could be the girl is a prostitute, and he's not happy with Renee encouraging the life by paying for her services. I think the last fits Adam's phrasing best, personally.