It's a wonderful novel that invents a history for Einstein's illegitimate daughter, about whom little is known. In the novel, she's a mathematician who becomes obsessed with her father's refusal to acknowledge her and twists her mathematical talents into a vehicle for revenge.
It is well known that prior to their marriage, Albert Einstein and Mileva Marić had a daughter whose history is unknown after she was put up for adoption.
It is also a well known, but controversial hypothesis, that Marić made important and unacknowledged contributions to Einstein's research. (As far as I can tell, there is no real evidence to support this hypothesis, but it is still a popular one in some circles.)
Combining these ideas, McGrail creates the character of the daughter's revenge for her father's theft of her mother's brilliant ideas. She is the sort of character who loves to "escape" into mathematics and grows from reading about mathematics for sheer pleasure to working on the Manhattan Project.