Post hysterectomy -biopsy. Right path?

Hi, My mother suddenly had severe abdomen and lots of sweating and shivering pain due to which she was admitted to hospital. Post ultrasound scan of the abdomen, they found that there is a 12cm cyst on the right ovary. Doctor asked us to admit her for a laparascopy for removal of the cyst along with the ovary. But during operation, the surgeon felt the uterus was unhealthy and took our permission and removed it [totaly hysterectomy]. Now they have sent the removed parts for biopsy and we are awaiting the results. While awaiting the results, the doctors are scaring us about cancer. The surgeon mentioned she is 90% sure it is malignant and asked us to wait for reports and meet the oncologist may be for some chemotherapy. But my concern is if the uterus and ovaries are already removed and are found to be cancerous, why should she undergo chemo? I am totally worried. please advise. And the CA-125 test count was 1500 before the surgery. Please advise. Are they going in the right path?