I read them in mind that obviously huge speculation is going to be made by the author. Of course its not going to be accurate, she is creating a story using timelined events as a frame.
Gregory's use of the folklore hereditary magic in the story line show readers how difficult it was to be a woman to have power. Jacquetta really did face trial for witchcraft on the accusations she that she had planned and arranged her daughters marriage to Edward IV. Men in power really didn't like women stopping their plans. Also fear of witches and curses was real. Gregory seems to use a What If- all the court gossip/ accusations did have foundation.
I agree with people about the incest side of things, I really disliked her Richard III affair with Elizabeth of York. Again she may have just wanted to show readers that intimate relationships between close relatives happened, but this is shown enough with all the cousin marrying cousins. And looking at it from a fictitous story point of view, it doesnt seem to fit in with the character she made up for Richard and the love his character has for Anne. It does seems a crappy attempt to build sympathy for Elizabeth of York leading onto the 5th book.