She looks too cut and paste, like she is floating above the walk path. The head is also anatomically off, with the face looking too large and far away from the rest of the head and neck.

An interesting concept, but the technical execution needs a bit more attention to detail.

You have so many sources, hard to find which one. It will help in the future if you title them such as "head and neck," "lungs," "wound," etc. instead of "Source 1," "Source 2," etc...

You're right, the body is unaltered from your source. It then becomes your overall composition that makes it seem too large and poorly placed within the image. This is a visual "illusion" created by the eye's movement from your other elements, colors, and value choices. But since your focus was a zombie effect, more than an optical illusion of distortion, I still stand by my last statement that your technical execution needs work to create a more visually believable balance of the elements used.