Mrs. Briar was into sorcery and dark magic. She served a master known as The Hunter, which was an evil and powerful shunken head. it's unknown whether or not she was a real witch or was just granted powers from the shrunken head.
For centuries, she was a Soul Hunter serving her Master The Shrunken Head. The way she would capture people souls, was to have them finish incomplete paintings. She would give them an imbued and cursed paintbrush. Then have them used nothing more than the same brush, until they would literally put their heart and soul into finishing the painting.
When the student would sign the painting, this would trapped them inside the painting forever. Also the painting would slightly alter. The slight alteration would be that one of the characters in the painting. The character would immediately change to fit the appearance of the trapped person inside. Doing this for centuries is was what enabling her to live forever.
In the 1990s she was defeated and destroyed when she tried to trap her art student Cody inside a ballet dance painting. What happened was when Cody signed the painting, she forgot to take the paintbrush back from her. When Cody broke it in half she escaped, and Cody burned all of her paintbrushes. This drained all the powers from the shrunken head and she was instantly defeated and destroyed too.