Billie was an Olympic figure-skater. Even back in the 1960s or 70s, Olympic athletes would have had the same frequent check-ups and health monitoring you'd imagine a professional athlete would receive. It seems impossible that no one would have detected diabetes until after her leg was literally rotting off her body—and then what the heck happened with the other leg? Moreover, diabetes requires life-long constant maintenance (particularly in an era before cheap, reliable personal glucometers), but we never see or hear of Billie taking medication or going to doctor's visits. The book almost seems to imply her diabetes was cured by amputating the affected limb.
Actually, she wasn't an Olympic figure skater, just that she could have been one, if she didn't need her legs amputated. While there were ways of testing for diabetes back then (the limiter strips to test blood glucose came in about 1963-65 and the first at home meter was in 1971), her exams and health monitoring would have mostly been physical, which can miss some of the warning signs, especially since urine or blood tests aren't included with your basic physical.
Billie mentions herself that she did not seek medical attention in the years she competed, and only became aware of her diabetes after receiving a scrape that refused to heal.
Billie: That small cut should have healed in a week or so. But it didn't heal in six months because the doctors found out I had diabetes. Would you believe my leg was rotting right before our eyes and there didn't seem to be anything the doctors could do to stop it. I hadn't been to a doctor all during my career. I suppose if I had known what kind of a vicious disease I had, I might have given up skating sooner.
A fairly minor nitpick: Audrina says that the First Audrina's playroom is filled with every sort of toy imaginable, while her own bedroom is bare. While we know that this is because she's really the first Audrina and all those toys are really hers, why couldn't they get her a few toys she could call her own? Was this part of the plan to turn her into the First Audrina by forcing her to play with the only toys available, or were they just too cheap to buy new ones?
Similarly (but also doubling as Fridge Brilliance), Damien's office is full of baby photos of the First Audrina, while poor Audrina complains there's not a single baby picture of her anywhere in the whole house. We know this is because the photos of the First Audrina are photos of Audrina, but would it kill Damien to say that some of the photos are Audrina, if only to reassure the kid that she's valued?
Was the Second Audrina born exactly nine years after the First Audrina allegedly died, or was she born on the day the First Audrina died? There's a minor plot point when Audrina realizes that neither Vera nor Arden would be old enough to remember the First Audrina if she was born nine years before Audrina's birth, but at other times it seems that the Second Audrina was born on the day that the First Audrina was killed (which would make sense symbolically, at least). The confusion could be indicative of Audrina being a very disoriented and Unreliable Narrator, or the conflicting dates could foreshadow the Gaslighting to which she's being subjected. But if you're trying to convince your kid that she has a dead elder sibling, and there's a grave in the cemetery with the "correct" date literally carved in stone for her to point to as evidence that you're deceiving her, you'd think they'd want to make sure the timelines match.
