This is an interesting literary project for the Whoniverse: a prequel to the career of one of the Doctor's companions. While I'm sure fanfic has produced speculation on Sarah Jane Smith's student days and early journalism career, and there is canonical evidence of the Doctor's encounter with Rose Tyler as a baby, this is the only example I can think of where the pre-Tardis life of a companion has been published between hard covers - indeed, in this case by her creators.
If you haven't followed the Big Finish series of Who audios, you may not be aware of Erimem, who accompanies the Fifth Doctor and Peri in a dozen adventures (plus one with Peri but no Doctor, a Telos novella, and two short stories in the Short Trips series). She joins Team Tardis in The Eye of the Scorpion as a forgotten female Pharaoh, fleeing internal conspiracy and alien invasion, and departs as the eponymous Bride of Peladon. The Coming of the Queen is the story of a few months in her life when she loses three brothers and her father, becoming consequently Pharaoh in her own right. The story has no sfnal content whatsoever (which must make it almost unique in the Whoniverse).
The story is essentially a murder mystery / political thriller, where the identities of the baddies are obvious from a pretty early stage. It's not Great Literature, but I think it is fun in its own right, as McLaughlin and Bartlett explore the roots of Erimem's loyalty and toughness as depicted in the BF audios. I suspect that people who actually know about ancient Egyptian culture will find plenty to complain about, but I am fortunately unburdened by such expertise. I would go so far as to strongly recommend The Coming of the Queen to Erimem fans, and I think even those who haven't previously encountered her will find it entertaining.