That doesn't work for me, she fights to the death everytime. Even tried going in with no weapons so that she doesn't get accidentally killed and it didn't matter, she still fought to the death, it just took longer.
Did you use knock down attack on her?
Also I failed everytime until I use Fane who is my mage. You probably need high Int because the character will change how it does the last part (no random just insert the bone back to make it fit then bandage it, the int char added copper wiring)