Melanoma is a very tricky and dangerous cancer and you appear to be in a rather “rare” category. First, there are cases where melanoma can mimic ovarian cancer. Second, it is less rare but advanced melanoma can be detected where there has been no evidence of a primary site.
My advice if you have not already done so is to have a second pathological review done and be sure to obtain copies of the pathology reports for your own review. Post results, you will get help understanding them.