YOU SAID:
I'm pretty sure she would have seen it through.
INTO JAPANESE
彼女はそれを見ていたはずだと確信しています。
BACK INTO ENGLISH
I'm sure she should have seen it.
INTO JAPANESE
彼女はそれを見るべきだったと確信しています。
BACK INTO ENGLISH
I'm sure she should have seen it.
That didn't even make that much sense in English.