Take a deep breath... I know, more easily said than done. Ovarian cysts are common and are almost always benign / non-cancerous (including large ones). Most resolve on their own, no intervention needed. However, yours is past that point due to its size so will need to be surgically removed. If the frozen section done at the time of surgery is benign, a surgeon with good cystectomy skills should be able to remove just the cyst and save your ovary or at least most of it. That will preserve the lifelong health benefits of the hormones it produces.
The ovarian cancer blood test, CA-125, is not accurate as there are too many harmless or benign conditions (including ovarian cysts) that can cause a positive / elevated result.
Although hysterectomies are very common, very few (10% at most) are necessary. Their prevalence leads people to believe that they are harmless. But that is not the case. The uterus, ovaries and tubes have LIFELONG functions. Removal of any one part has been shown to cause permanent, progressive harm including increased risk for a number of health problems.
The uterus is an anchor for the bladder and bowel and important for proper function of those organs. It's also essential for sexual function. Its ligaments are the pelvic support structures hence the torso collapses after hysterectomy. That's why hysterectomized women have a shortened, thickened midsection. Studies show a 3x risk of heart disease after uterus removal. A recent Mayo Clinic study shows increased risk of heart disease and metabolic syndrome. Many women also report blunting of emotions / loss of connection with others after removal of their uterus.
Removal of female gonads / ovaries (even after menopause) or their failure after hysterectomy has been shown by many medical studies to accelerate aging and increase risk for a number of chronic conditions such as heart disease, stroke, metabolic syndrome, dementia, impaired cognition and memory, parkinsonism, mood disorders, lung cancer, osteoporosis, aging of skin and eyes.
Despite a benign frozen section of my cyst, my gynecologist removed all my female organs. I was 49 years old. The effects turned my life and health upside down in a matter of months. That was 12 years ago and not a day goes by that I don't mourn all the problems it's caused. I'm on estrogen but no cocktail of hormones and/or supplements can replace what an endocrine gland does so wondrously. Believe me... I've tried everything to restore my youthful looks and pre-hysterectomy self.
My connections with hundreds of other women and information I obtained from the HERS Foundation made me realize that these after effects are typical.
I hope this helps and I hope you can get proper and ethical treatment (removal of just the cyst if it's benign).