Scholarly attitudes on transgender people involve a difference of opinion and seem to be evolving. While traditionally being transgender is considered haram, some modern scholars do not consider being transgender as haram, instead treating it more along the lines of a medical condition.
The trangender female narrative tends to follow the lines that Allah made this person innately female, and there was a biological mismatch at birth. With this interpretation, hadith such as
The Prophet cursed effeminate men (those men who are in the similitude (assume the manners of women) and those women who assume the manners of men
Sahih al-Bukhari 5886
imply that it's haram for a transgender female (who genuinely believes herself to be innately female) to impersonate a man.
The other argument main against transgender people is it's changing the creation of Allah (Qur'an 4:119), but from a transgender person's perspective, it can be considered as correcting a biological defect (which is permissible in Islam).
So there are respectable justifications one might not even consider it a sin.