the lady's disembodied right arm

Now if it were "disarticulated" it would be technically more accurate, and more obviously inappropriate. For me "disembodied" carries with it a feeling of "...yet intact in all other ways, and even functional," which isn't present in the usage you cite.

(Or, in fewer words, Yes, I think it's strange, too. [But that's probably the reason the author chose it.])