The obvious comparison is to Bull Endurance, which is the same price and has the same expected value of "healing."
Bull Endurance is better against Taint, and never rolls low.
Healing Charm has 2 keywords, triggers the Priestess's life gain special ability, is much more resistant to dispel, and can maybe roll high.
All told, Healing Charm is probably a smidge better, mostly on the strength of dispel resistance. Once it's revealed, a dispel isn't going to kill your creature, like it could if Bull Endurance was the only thing keeping your creature alive. I don't know if that means it's good enough to play in a competitive book.
I don't play Bull Endurance in my Beastmaster deck, even though it would be nice to let Fellella cast healing spells (especially under the circumstances where I normally would cast Fellella). But maybe a Priestess deck has a use for more healing?
In the abstract, though, I think I would prefer to play any of the following: Vampirism (enchantment or Vampiress), Regrowth (Belt, Gorgon, Unicorn), Death Link, Hand Of Bim-Shalla, Lay Hands, Drain Life, Drain Soul, Wand of Healing, Blood Reaper, Block, Reverse Attack, or Rhino Hide.
If none of those are suitable, maybe give Healing Charm a try?