>>6608079The most thing you can do is to make sure she's well-informed on the matter; show her statistics and empirical evidence to ensure that she is making a sound decision.
A lot of people nowadays seem to incorrectly believe they're transgender to run from other issues in their lives, most notably among which, the possibility of subconsciously viewing themselves as a failed member of their own gender - a link which multiple studies have demonstrated. Show her how the suicide rates don't change following SRS, how the surgery physically works, and of course make sure she is not running from the fact of how there's no going back.
Try to have her see a sensible and understanding therapist to rule out the possibility of other factors in her life making her possibly incorrectly think herself to be trans, and encourage her to wait a few years if she is still young. If she truly and firmly does believe that she is transgender, then give her as much support and love as you can, but at the same time urge her to be realistic - warn her of the very psychologically damaging effects of setting unrealistic transition goals for oneself, and against becoming sheltered in transgender communities, which can very often act as toxic echo chambers.
But more than anything, love her. She is still your sister.
