What is unique about Ultima, and about this novel as well, is the power that Rudolph Anaya gives to nature. He does this by empowering Ultima with plants and herbs in her different treatments and remedies.
She harnesses the power that nature has and then uses it for good. This is special because she can do it, but also because she sees the value and power in nature, which so many people in the book and outside of the book (think about the real world), do not see.
Her power is not only obvious in her remedies, but also in how people treat her. She has a few people, like Antonio's family, who are devoted to her and believe in her powers. But there are many in the town who fear her because they know how powerful she is.
Overall, Ultima believes that nature has the power to do God's work and she has learned how to harness that power to do as much good as she can.