Yes. In the United States being a citizen provides protections within the USA. I don’t think she would lose her citizenship, I’m not even sure it is constitutional. Perhaps they could charge her with treason and that is an avenue under “the big 7”. We would be more likely to let her remain a citizen and charge her with crimes that would lead her to a long term prison term. As for the UK, I hope they handle the situation well as it will have potential long term consequences.