It's carried down through the moms. They say that 50% stuff because they really don't want to give out the true stats. I have BRCA2. All I can for you is to start getting mammograms now. Find an OB/GYN that takes it seriously. Trust me, I know. With both grandmothers and mom and sister having cancer, I had to go through several dr's until one actually listened. Sucks, I know.
Anyway, your mom is probably totally freaking out because back when, cancer seriously turned your life inside out forever. Nowadays, expect your body not to be your own for a year or so. And you learn what kind of chutzpah you're really made of. It's difficult and I'm rooting for both of you.

Average, for horses with some experience at this level