the enemy is indeed quite tough, but it is an optional encounter with little reward if you do kill her. the opening fire ball is indeed quite nasty, but it can be dealt with. there are some other enemies that are designed as well in that direction for example the trolls, but again they are optional.
personally i would not change the encounter, but drop a bit of game lore that hints at her strength and weaknesses, e.g. a book that describes her tactics if you loot her home in the driftwood fields (similar to the troll books).
