"Winter's Heart" was about five books ago, and Birgitte had repeatedly mentioned that her memories of her prior lives were fading. In that case it would make sense that she would forget all of the times the sword was not a good selection for her if she needed to use it - I think the important thing about her POV from that "Winter's Heart" chapter is that it was implied that she chose the sword multiple times and I think it was because in those other lifetimes, that was the best weapon to use, even if she almost got killed. That's why I think the same situation is going to come up soon.