35 years old with Ovarian Cancer is not rare and, for me, raises concerns about the doctor if that is what the doctor is saying.
If you research this site, you will see that there are many young women diagnosed with this disease, I was in my 30s, I know of women in there 20s. Cancer knows no age.
The conditions, as far as I know would not be related to eachother. From what I saw, molar pregnancies have to do with the uterus.
Is your daughter in law being seen by a GYN/Oncologist? How do they know it is ovarian cancer? Has she had surgery, a biopsy? A CT Scan, sonogram? CA125 blood test?