She's very young to be making such a big decision, but it is her body and her choice-- a few years ago it probably would have been considered a much more drastic course of action than it is now. Even if she doesn't have a significant genetic risk, she's not the only young woman wanting to eliminate what she obviously sees as a big threat in the future.
Aside from breast feeding if she wants to have a child at some point, taking that path may make little impact on her life if, and this for me is the big if, she is mentally prepared to face the fact that reconstructive surgery is often sub optimal and there is no assurance that she will be satisfied with the results. If that's what she chooses to do.
Counselling is a very good idea but even if she delays the decision for a couple of years, will you be anymore comfortable if that is her choice when she is 34 or 44? Her age is a factor, but she is an adult who has already been through a traumatic experience and it's understandable that she wants to avoid a repeat performance. As the others have said, it won't necessarily change her chances of metastatic disease, but it might stop the feelings of doubt, mistrust and uncertainty that are currently making her miserable. Mxx
