@Omniscient Reader she visited his grave in one of the recent chapters. it was the whole reason everyone in that family was distant and competative before her arrival in that world.
@Omniscient Reader it was mentioned early on as the reason the original Tara locked herself in her room and ate sweets all day(the reason she was fat at the beginning), she became lethargic because she blamed herself for her brother's death. it's also why she had such a hard time convincing any of them to do anything early on.