The ways of the Hamne were still so foreign to her people, they had only been conquered by them ten years earlier - their customs were strange and they never seemed to act as one assumed they should.
This is indeed strange. Recall that according to the story, Hamne’s warriors selected the princess (calling her the princess because her name wasn’t provided) to be their new leader, because she “defeated” or rather back stabbed their leader Brackhan. I would imagine Brackhan had some sort of next of kin and getting rid of Brackhan would free his place as a tribe leader. Realistically any medieval tribe would immediately execute her, of course, not before letting her have it with all the lieutenants in the army. That’s what her people would do and that’s why She closed her eyes ready for her coming death
It is even more surprising that Hamnes were a nation of conquers somewhat similar to Vikings, I presume. So even if they would spare her and give her some sort of an honorable position as a civil governess, they wouldn’t accept her as the head of their army without a military experience. Cutting the heart from one man’s chest I don’t think would qualify.
But then again it’s flash fiction and you don’t need to tie this scene down to anything at all.