YOU SAID:
Not sure why she drinks.
INTO JAPANESE
なぜ彼女が飲むのかわからない。
BACK INTO ENGLISH
I do not know why she drinks.
INTO JAPANESE
私は彼女がなぜ飲むのかわからない。
BACK INTO ENGLISH
I do not know why she drinks.
That didn't even make that much sense in English.