- Notice that the flashback to Ashildr's memory of losing her children features three empty cradles, not one, and her diary's wording suggests that all her children died within days or hours of one another. Of course it does: if only one of her children had been dying, she'd have used the spare implant to save them, but with three of them sick simultaneously she'd have had to choose between them, then live with that choice forever.
- Also they were infants. Ashildr stopped aging when she became immortal leaving her eternally as a very young woman barely out of her teens, using the medkit on one of her children would trap them in the body of an infant forever.
- After 800 years of life it seems unlikely that Ashildr had only had children in one 'regeneration'. The pages torn from other books may have been times when other children died. She kept the last time to remind her not to take that risk again. Part of the horror for her may be that she doesn't age with her children; She'd have to leave them at a young age so that she wouldn't give away her secret. Being separated from her children, possibly watching them age from a distance, never being able to save them from death... No wonder she became so cold of heart.
- Odds are a young woman in a Viking village would not know how to read and write. Ashildr most likely first learned how to read and write when she realised her memories were fading.
- It's hardly a surprise that Ashildr would remember Clara, even after all this time: she's probably run into a bunch of Clara's timeline-scattered duplicates over the centuries.
- The Doctor's speech about how long-lived beings benefit from having short-lived ones for companions isn't limited to him and Ashildr. Of the various other renegade Time Lord characters we've seen or heard about who were genuinely wise, good, and/or happy with their lives, K'anpo Rimpoche had his (human) monastic disciples to keep him grounded, and Word of God states that the Corsair kept parrots and cats as pets. Even the Master tends to keep non-Time Lord lackeys and catspaws around, and Missy's posthumous conversations with new arrivals to the Nethersphere may have served the same purpose of keeping her aware of mortality.
See the Series 9 headscratchers page.