Here are some options you could use:
Formal:
* Magician: While technically gender-neutral, this is often used for both male and female magicians.
* Sorceress: A traditional term often used in fantasy contexts.
* Enchantress: Another traditional term, often associated with magic and spells.
* Witch: While often associated with negative connotations, can be used neutrally.
Informal:
* Magicienne: A French word for "female magician".
* Female magician: This is the most straightforward and clear option.
Ultimately, the best word to use depends on the context and tone of your writing.