Major abdominal surgery suggests removal of organs for things like ovarian, cervical, colo-rectal, uterine, kidney or adrenal cancers. Of course, there are other possibilities. If she underwent a debulking procedure, using the term preventative chemo would not be at all responsible as there would definitely be cancerous tissue left in place. Cancer can be confined to an organ if caught early-ish but not offering/accepting precautionary chemo would be unusual if the pathology report indicated malignancy and CT/MRI/PET scans showed no areas of concern for metastasis. Tough to imagine her not getting the best care available to anyone anywhere, ever.
https://www.cancer.gov/about-cancer/diagnosis-staging/staging