Later there was jealousy for Ludwig II, who preferred Sisi to Sophie.
Indeed, they were not that close. Yet they had, as most of their sisters, a tragic life(Queen Marie of Napels, Nene, Sophie, Elisabeth - as far as I know), and a tragic death. Sisi was, as everyone would be, completely shocked because of Sophie's death(in one of my book it's beautifuly mentioned - fiction but really good: Ludwig II, who has died, apears to Sisi and mentions one of their loved-ones will die and that the three of them will share eternity. Later Sophie dies and Sisi realises her end is becoming near. Fiction as I said, but really beautiful. The book really shows how complex Sisi's character was.