My wife is suffering from lower abdominal pain and she is bleeding on occasion, what could cause that? Her doctor told her it might be fibroids.

Fibroids. Uterine fibroids manifest as vaginal bleeding, not abdominal bleeding (rectal bleeding). Please revisit with your doctor.
Lots of things! Her symptoms are non-specific, but concerning. Gi-related problems can originate from the small intestine (crohn's, infection, partial obstruction), the colon (colitis, appendicitis, tb, altered motility), the kidney & collecting system (ascending infection, stones), ovaries, tubes, uterus, hernias that may contain bowel, bleeding, abscess...You get the point. Have her seek evaluation/treatment.