Peace, everyone.
I need a little help here. I was talking to my aunt a few minutes ago, and she's a typical Sunni who believes in all ahadith. While discussing, she told me that the Qur'an was not in the form of a book until Abu Bakr and Umar decided to compile it into a book. Then she said that the prophet Muhammad (pbuh) had left them the information about the correct way of arranging the surahs which as we have it today. And she implied that the knowledge which Muhammad (pbuh) received on arranging the surahs, came to him as a revelation OUTSIDE the Qur'an through Jibreel. Unfortunately, I couldn't answer her back because of my lack of knowledge on this topic.
Right now, I only remember - "...and We have arranged it well in arranging." (25:32)
So of course, it is God who has arranged it. Now my question is, if Muhammad (pbuh) didn't receive revelations outside the Qur'an, how did God made the arrangement of the surahs while He was revealing the Qur'an to Muhammad (pbuh)?
I need you to put your thoughts here for my question with Quranic proof (if possible), cause I really need to reply to my aunt and also to learn for myself.