I would say that the line which would most strengthen the reflection in Kara's essay if it were added after sentence 4 is the following one:
After unintentionally breaking my roommate's treasured figurine, I squared my shoulders and took responsibility for my actions, much like my little brother had done all those years ago.
After sentence 4, it would be a good option to write about what exactly happened that prompted her to admit that she was the one to do it. The other options are all the same - they all talk about her brother and how she wishes he were there with her.
