Neville, here are some sources on true threat of suicide being pikuach nefesh vis a vis violation of issurim.
Emek Halacha, from rav Yitzchok zilberstein, 205-209.
Rav shlomo zalman writes that since the mother’s mental condition can be treated with therapy, we don’t allow abortion
1( English Nishmas Avraham, Choshen Mishpat, 425:11, p. 288.)
But rav shlomo zalman would agree that if the therapy isn’t working, as is the case with many of these gender delusional people, that it would be allowed if there is serious fear of death