User blog comment:Edrea/Is Morgana more powerful than Merlin?/@comment-5674726-20130628163633

Morgana wears a healing bracelet with powers that are allegedly without equal in the Five Kingdoms - for comparative purposes, the Sidhe, who Kilgharrah claimed would be able to heal Arthur, are in the Five Kingdoms, which would make her bracelet more effective at healing her than the best option available to Merlin to heal Arthur from a similar wound. It's unlikely that it's only good for blocking the dreams of a Seer, especially as she would have known that it would be of no use to Alator of the Catha if that was the case.

One theory I have is that it works by attracting healing magic when it is needed - Morgause's when Morgana was poisoned, Merlin's (and Kilgharrah's, by extension) when she fell down the stairs, Aithusa's when she was dying in the Season Four finale - and perhaps by storing that magic until it's needed, so it gets more powerful.