So, I 100% did not understand the end

[Claire]

Ok u guys! Explaiing time because the last 100 pages of this book were a blur to me...

[Kristin]

She could choose the selfish choice: the young girl. That's the easy choice, what she's always known, and continues to foster the evil that the Physician thrives on causing.

Or, the other choice was to sacrifice herself by taking an evil life, a body that wouldn't serve her well, preventing the death of others. Choosing that man also protected her family but also would have kept her from the love she had with Dex.

She chose the (more) selfless option. Because she did not follow the Physician's path, the brujahs were able to fix Annaliese, putting her (sorta) back together and returning her to the life that helped shape her into the girl who would make the right choice.

That was how I explained it to myself.