I found this in my Goodreads recommendations feed and thought I would give it a shot and as it turns out I enjoyed it more than I thought I would.
Firstborn Academy trilogy is set in a post-apocalyptic world where humanity in nearing extinction. They share the Earth with their enemy who are an alien species called World Walkers. The story revolves around Nora who is the firstborn of her family and as per the treaty/agreement with the World Walkers has to be shipped off to them for reasons unknown at the time.
This is a short trilogy where you could easily finish all three books withing a day or instead what I did, read one book at a time before heading to bed. Enjoyed the 1st book and the 2nd book. I also enjoyed the 3rd but not as much - I felt the ending was a little rushed and I would have liked to have seem more development around the new characters introduced.
In short, recommend give this trilogy a read.