YOU SAID:

I was trying to remember when does my sister started to turn into a woman

INTO JAPANESE

私は妹がいつから女性に変身し始めたのかを思い出そうとしていました

BACK INTO ENGLISH

I was trying to remember when my sister started transforming into a woman.

INTO JAPANESE

私は妹がいつ女性に変身し始めたかを思い出そうとしていました。

BACK INTO ENGLISH

I was trying to remember when my sister started transforming into a woman.