Hi sessibo,
blood in your stool can be very serious it could be anyone of the following:
bleeding ulcer
gastritis
esophageal varices
mallory-weiss tear
diverticular bleeding
vascular malformation
intestinal infection
inflammatory bowel disease
tumor
colon polyps or colon cancer
hemorrhoids
anal fissures
not to say that your fiancee has any of these but just to be sure i'd rush over to the er and get it checked out just to be safe, because blood in stool usually indicates an internal problem that was probably not caused by any pulled muscles in the stomach. Hope everything is alright.
Tanya*xox