How come this Threnvale Kingdom didn't become an invasion target by neighboring countries before this, with how shitty they treated other country's envoy? Granted she's their kingdom's former citizen, but with royal correspondence letter and that scale, at least they'd considered her somewhat legit. Disrespecting an envoy had been a source of casus belii for war declaration for a long time, since it's almost the same as you disrespect both said country and its monarch/goverment.
Ask Mongol Empire's conquered people what happens when you disrespect a Mongol envoys.
And Stephan (her former fiancee's little brother) is a psycho sadist (he even got entushiastic about beheading someone...), this kingdom's future is doomed. overthrowing the royal family and their nobles seems like a merciful option for them.