I am curious if your girl has had any cesareans or other abdominal surgeries prior to her spay?
"Adhesions" might be the cause.
Ask your Vet...
Here's a definition of what adhesions are in the human form but, animals can have them, too.
http://en.wikipedia.org/wiki/Adhesion_%28medicine%29 Small bowel obstruction (SBO) is another significant consequence of post-surgical adhesions. A SBO may be caused when an adhesion pulls or kinks the small intestine and prevents the flow of content through the digestive tract.