In Hild, the main character is considered by many to have supernatural powers of prediction, but you make it clear that she's using her acute observations of the world around her to make these predictions. (Sort of a medieval Sherlock??) Is this a writerly invention, or is it based on something you found in your research?
All we know of Hild is the tiny bit Bede wrote 50 years after her death which isn't much. The first half of her life can be summed up in one short paragraph. She is born circa 614 CE, after her mother, Breguswith, has a dream about her unborn child being a jewel that brings light to the land. Hild's father, Hereric, of the royal house of Deira, was poisoned while in exile at the court of Ceredig, king of Elmet. Her older sister, Hereswith, marries a nephew of Rædwald, king of East Anglia. Hild, along with many of Edwin's household, is baptised by Paulinus c. 627 in York. She then disappears from the record until 647 when she reappears in East Anglia about to take ship for Gaul to join her sister—at which point she is recruited to the church by bishop Aidan.
We don't know where Hild was born exactly and when her father died—or her mother. We have no idea what she looked like, what she was good at, whether she married or had children. But she had to have been smart, blindingly smart, to survive so long and so well in what was essentially a time of warlords.
One of the things I guessed she was good at was out-thinking others--in other words, she could predict what they would do. So I gave her that skill. Then I just how to work out how she did it. Given the centrality of the natural world, I chose that.