Chris Chibnall could do the same with this supposed past female Doctor, introducing a fabulous guest-starring actress who would possibly be the female Doctor that preceded Jodie Whittaker.
While there’s no exact precedent of female Doctor on Doctor Who, there is precedent of former showrunners retroactively creating different incarnations of the Doctor outside of the numerical set.
John Hurt’s War Doctor was created by then-boss Stephen Moffat for the 50th anniversary special, despite the fact that past lore had never made reference to him.