Confused and scared - sister diagnosed with peritoneal cancer, unable to find the primary

My sister is currently in hospital cancer has been found in her peritoneum they can't find the primary yet and have taken biopsies, ovarian cancer suspected , also when collecting biopsies it was discovered that her peritoneum had fused with her bowel and pelvic region , lm so scared what her prognosis will be , has anyone any experience or advice about this ?