[mjm]

My understanding is that medically the 2 options have similar enough outcomes that it really comes down to what the woman feels most comfortable with (unless a mastectomy is medically required). It may help her to discuss all her questions and concerns with her doctors (and maybe get additional opinions) so she can be really clear about the risks and benefits and details of each option.

But ultimately, the decision should be hers as its her body.

Best wishes to you and your sister.