First off it looks really awesome and I love the idea that she can shape her tail into differents forms.
I think the deltoids of her tail (wow, that sounds weird XD) are a bit too flat and the different sections of the abs are kinda the same size in your image, whereas in reality they differ in size.
The deltoids on the main character look okay to me. Maybe the trapezius would reach up a bit higher towards her head.
Hope it helps and makes sense. ^^