Three hundred years ago, while living in Salem, Massachusetts, Ms. Mystic was dubbed a witch because of her ability "to help people" psychically. Although burned at the stake, she was able to remove her "essential body" from her "mineral body" and inject herself into another dimension. There, she waited for some force to release her.
That force came in the modern day when a psionic converter being used by a group of scientists from the Science Investigation Agency bridged the gap between the two dimensions and brought her back to earth. One of the more unusual achievements of artist and writer Neal Adams.
In addition to being able to heal the sick, Ms. Mystic can fly and generate destructive energy blasts by tapping the power of the earth and channeling it through her golden sword and golden antennae, controlled by the heroine's will. No explanation for these weapons, or her costume, was ever tendered.