Based on the traditional "evil witch" stereotype:
* Good fairy
* Angel
* Saint
* Benefactor
* Friend
Based on the modern, more positive interpretations:
* Wise woman
* Healer
* Shaman
* Mystic
* Spiritual leader
Based on the negative connotations of "witch" as someone who uses magic for harmful purposes:
* Benefactor
* Helper
* Friend
* Guardian
Ultimately, the best antonym for "witch" depends on the specific meaning you want to convey.