I should have clarified, I'm no Jo Cameron. I'm no different from your average person in how I feel physical pain and empathy. It's extremely rare to have what she has, I think there are only a handful of people in the world that have that. What's far more common, and what I believe I have (and what a few other people in this thread have) is a double FAAH mutation. (That makes up the relentless positivity and lack of fear parts of her personality.) I can't find any estimates on the frequency of that, but around 20% of people have the single FAAH mutation that is basically a less strong version.
The discussion about empathy is an interesting one. But I think treating it like it's some genetic binary thing is completely the wrong way to see it. Empathy, in some ways, is a cultivated skill. The Nazis were elected. Does this mean that Germans were born with less empathy, unable to empathize with the Jewish, disabled, Roma, queer, etc? No, it just means that society succeeded in turning them into an Other who nobody could empathize with. That is to say, I think that if you gave two identical twins entirely different upbringings they would end up with different kinds of empathy. So I think sure, perhaps Jo Cameron doesn't have some of the genetic material for things we may associate with empathy, but she seems to have taken on many empathy-adjacent values like selflessness and really caring about others.
I think the thing with the daughter is just teenagers being teenagers. Having been a teenager once myself, I wouldn't read too far into it :)