Complex sentence: Talisman cannot remove the Coronet without it causing her severe mental pain (and it took a great effort from others to remove it), however if someone else wears it, returning the Coronet to the true owner would spare them the pain.
Split into simpler sentences: Talisman cannot remove the Coronet without it causing her severe mental pain (and it took a great effort from others to remove it). However if someone else wears it, returning the Coronet to the true owner would spare them the pain.