YOU SAID:

I told my sister I could beat her up. She said, "No, you can't." so I started to beat her up, but before I did too hard, I thought, "Wait, why do I need to make my sister know I can beat her up?"

INTO JAPANESE

私は彼女を打ち負かすことができると私の妹に言った。彼女は言った、「いいえ、できません」。それで私は彼女を打ち負かし始めました、しかし、私が一生懸命にやる前に、私は考えました。

BACK INTO ENGLISH

I told my sister that I could beat her. She said, "No, I can't." So I started to beat her, but before I worked hard, I thought.

INTO JAPANESE

私は彼女を倒すことができると私の姉に言った。彼女は言った、「いいえ、できません」。それで私は彼女を殴り始めた、しかし私が一生懸命働く前に、私は考えた。

BACK INTO ENGLISH

I told my sister that I could beat her. She said, "No, I can't." So I started to beat her, but before I worked hard, I thought.