Did you have the genetic test? Sometimes when they test a couple hundred genes, they come across one. If your mom had one done you would have the readout from both your tests.
I do know it is easier once all tests are done and the suggested treatment plan is put in front of you. I had Brca2, so i did elect taking off the other breast. I did not want to think cancer could come into that one. Wait did not work for me.
Let the medical team give you choices. Maybe talk to your mom more about her feelings with her cancers if that is possible. For sure come back here and keep us posted, so we might support you on this tough journey.