Umm, makes perfect sense, she was/is one of three Goblin leaders.
...who was killed far away from their camp. How would they know 1) that she was killed at all and 2) that the player betrayed her?
It would make a lot more sense if she made a point of sending a runner (that you could try to intercept) back to the goblin camp with the news and sending for reinforcements or something. Though Minthara seems sufficiently overconfident that she probably wouldn't do that.
