Because she is likely to be prosecuted here in the US. I believe she is trying to flee the country. Either she was going to fake her death (plane crash) or because Vietnam is one of the few countries the US doesn’t have an extradition treaty with she could just stay until Vietnam kicked her out and she would disappear to some tropical island never to be seen or heard from again.(If they don’t have actual crimes against her, that would be ok as well but she has to be guilty of more than just being stupid.) https://www.zerohedge.com/political/kamala-harris-departure-vietnam-delayed-over-alleged-havana-syndrome-incident