It seems awfully coincidental that they both have birthdays on significant dates, and we have only dealt with the consequences of the temporal issues of the NeverNever as regards Rashid’s aging and Murphy’s absence in Proven Guilty, but we have been reminded since the NeverNever was introduced.
She was in the control of Lord Raith for Thomas, so this is suggesting he was trying to breed a Starborn with Wizards powers and a hunger demon. Given the reproductive issues Whampires have, conception could not be guaranteed for a particular time so Margaret with her knowledge of the ways would have been the only option (other than Rashid, ruled out for other reasons)