We know nothing about her!
I want to know if people have any theories.
So, I shall ask some 未回答的 questions..
..unless they have been answered already, and I've just forgotten.. xD
These 问题 could possibly be answered in the 下一个 3 books. ;)

So here are the questions:

1. Who was Reyna's father, and why was she at Circe's Island and not with him?

Bellona had two children from the same man, so maybe it's normal for Roman demigods...
I think he could've died when they were children, so Bellona sent them to Circe's Island.
...Or maybe their father had arrived at Circe's Island when Hylla and...