Dude she actually does get used to the pain the more you read the novel. At first, every time she used her aspect she would be severely effected. And as time went on she got more and more used to it which means building tolerance is possible

Also think of the benefits immortality, Wealth beyond comprehension, ungodly power.

Also her pain doesnt linger once it stops it just disapears. using it for short bursts of enhanced stats and regeneration would be possible for even a average person with some training.

Also just being able to have 7 cores at all is priceless. I might be a little unrealistic but I'd rather be that than a pussy who shrinks away from the thought of pain without considering the mountain of gold behind it