And as soon as I did that, I found that I had had the heroine do something stupid for no reason. There were more prudent directions for her to take.
So I think a bit and it's trivial to give her a motive, namely seeing something menacing in the other direction. Fortunately it's not very stupid. Still I didn't get far today.
And I still have to decide if she decides, with hindsight, that she imagined it.