You’re correct that mastectomy is gender-affirming care for people who are trans, but it is also healthcare accessed by cis people to prevent or treat cancer, just like hormone replacement therapy is used to treat menopausal women and puberty blockers are used to treat precocious puberty in cis children. The point I was trying to make is that cis people have access to these treatments despite them often being labeled as a “trans thing,” not that any of these are exclusively gender-affirming care. However, I do also want to note that gender-affirming care is legitimate healthcare, and choosing mastectomy to lessen dysphoria is no different than choosing the same procedure for peace of mind regarding one’s future breast cancer risk.

I’ve seen no GC women condemning Pin and many supporting her. In fact, as has been discussed in the comments here, her abrupt turn to anti-trans rhetoric seems at least in part an attempt to summon supporters from GC Twitter to back her up.