I loathe how much she pampered to the Horde on that day. You're one of the most talented sorceres -Ice Nova everyone and make them listen. Promise to father that you'll personally freeze and shatter any hordie that goes back on non-aggression deal. Follow up on your promise. Problem solved.
But, despite this she is NOT responsible "for death of our king, and a lot of our people including your cousin and couple of your friends". She didn't side with orcs, she didn't kill anyone. She didn't put them into that fight. Quite the opposite - she tried to stop this fight from happening. All she did after that - is to stand aside. And while, again, I think it was idiotic, the only ones responsible for deaths that day were people charging into fight and Horde killing them.