Except the majority of Sejuani's people jump on on broad to support Ashe...in fact pretty much all of them turned their backs on Sejuani because so far all she did was talk and care about her "destiny" rather then do anything for her people.
It was her fault for not taking initiative earlier, instead focusing on her training to extend more pointless fighting that was doing nothing for the people as a whole. She threw a temper tantrum rather then figure out a way to help her people and slap away any efforts that could have helped her people.
And I find it odd that you think civil fighting was a GOOD thing considering that Noxus just recently had to put down their own division within their own city-state.
So shouldn't that mean that Ashe proved herself that she managed to do something that no one else had accomplished for generations? She united her people, whether by force or by diplomatic means is irrelevant, she did it.
And war is an ugly thing sure... but when there´s not food for everyone, i guess it is the only way.
And Sejuani doesn´t come to me as a brat moved by "her destiny", read her bio...
It just seems to me she just want to feed her people... They trust her to get them out of the ground (or so i thought).