Thanks, that is helpful, as looking closely at this has changed my view on the topic somewhat.
It still doesn't look to me as if she is being strangled (is it absolutely agreed by all critics of the painting that she is? I know nothing about the work or the artist so will absolutely cede to anyone's superior knowledge here).
But anyway she DOES look to me, on closer inspection, that she is bound around the neck and waist with a rope, is that right?
To me that changes it from a straightforward nude to an image of the degradation of women - and it's a sad fact that such imagery is often also a feature of pornography.
Discussion of this would be fertile ground I am sure, but not for none year olds. So for this detail I do agree the picture was inappropriate. (Though I wouldn't phone up to complain as teachers are human too and most do a great job, so my bar for complaint is very high - I'd just discuss it with my child and try to reassure them if it raises any questions for them).
I'd still like to know more about what the topic was, what was said to the children about the picture, whether they were asked to copy it or produce work inspired by it, etc etc