Is it really casual nudity when the individual is nude in a location/activity where it's expected that they be nude?
It might be more of a meta reasoning. Most of time nudity around here has a sexual implication, but here it's just "she's in the shower" so it's casual instead of implying anything.
However, I think this doesn't really qualify because the image is very clearly intended to be suggestive in a way that true "casual nudity" images are not. Just look at the posing and the facial expression.