Under the Broken Moons (2015)

From the introduction:

In a couple hundred years from now, earth is threatened with global disaster. Humanity flees to space in a huge generation ark. Some are left behind. Thousands of years later, the ark ship automatically returns to earth, but things have gone wrong. The ark people have forgotten their past. The ship deconstructs in orbit into a series of orbital rings and the humans are evacuated to earth. This, the escape pod, is the Tomb of the Barbarian. The ark people, the Visitors, have evolved differently from those who remained, the Children of the World. The Barbarian was able to access and understand the pre-apocalypse technologies and wield them; the title is an ironic misnomer. She was able to use both Visitor technology and Children magic. For this reason, she was feared and revered.