> You can’t just leave the country and expect the new host to not care!

That's not a fair comparison. If any law was broken, it was definitely not broken on US soil. It would be like US arresting people that it thinks committed murders in China.

> What she is alleged to have done would be a crime in Canada too so her nationality isn’t relevant.

I think it is. It's also relevant where the crime occured. e.g., lets say some small country decides that it's illegal to wear grey color pants. Then, can they morally arrest any person anywhere in the world that they think wore grey color pants at any point in the time at any place in the world?