My mother in law is 89 years old and she just told us she is bleeding internally from her intestines? What's the usual treatment?

Depends on source. Need to find the source and the cause. Can be due to polyps, tumors, fragile blood vessels, infection, inflammation, poor blood flow, hemorrhoids. Might be coming from stomach: see above, but also ulcer disease. Treatment varies with location and cause. Sometimes can be taken care of pretty easily with colonoscope-polyp removal, cautery; sometimes meds or radiology rx; sometimes needs surgery.