In monarchies the people don't matter at all. Also Terenas only send the messenger to falric and Marvyn to retreat as so he didn't define any orders, murdering your father is a conmon thing in mediaval monarchies to take his title and few times in history after they took the title like that they renamed the country and said the previous country was no more. So we can see here killinh the previous monarch doesn't make you lose the land. Also before becoming the LK arthas was as much as undead as necromancers in wc3 were.
https://wow.gamepedia.com/Brother_Anton_(quest) he had a quest withing which he sents player desolace to meet another Scarlet crusade member who was friendly to the alliance. Old wowsite "The League of Arathor, the remnants of the once-proud kingdom of Stromgarde (now occupied by ogres and the criminals of the Syndicate), would claim the basin to profit their allies in Stormwind" and only dialogue its leaders say about stromgarde"The League of Arathor has sworn to retake Arathi for humans of Stromgarde and the Alliance. It is a battle hard fought, but a battle worth fighting." Meaning they do it for the humans of stromgarde not for the kingdom nor its king. Well they might no be rebels, but they are traitors as word of god said" The League of Arathor seeks to reclaim the lost land of Arathi Basin for their benefactors in Stormwind" meaning they want to give it to SW.
She doesn't know that the child might have not disrespected him thar much while alive.
Its normal to yell to disrespectful child.