Ovarian Cancer after total hysterectomy

My mother had a total abdominal hysterectomy in 1974 at age 41.  Both of her ovaries were (supposedly) removed.  She became menopausal and was prescribed Premarin.  

Fast forward to 2003... in July my mother was diagnosed with metastatic adenoma.  We were told that she has mets in her lungs, liver, pelvis, and long bones.  The primamry is beleived to be a mass in abdomen. Her oncologist says that it appears to be ovarian in origin, probably from "ovarian cells" which were left behind when she had her hysterctomy.  Is this possible?  What is the usual treatment and prognosis?