YOU SAID:
She wasn't at the herosan's party that she went to
INTO JAPANESE
彼女は行った英雄さんのパーティーにいなかった
BACK INTO ENGLISH
She wasn't at Mr. Hero's party.
INTO JAPANESE
彼女はヒーローさんのパーティーにいませんでした。
BACK INTO ENGLISH
She wasn't at Mr. Hero's party.
That didn't even make that much sense in English.