Arya finally manages to kill the Waif. She achieves this by leading the Waif to Arya's hiding place, where Arya keeps her sword Needle. She then cuts the candle off, and taking advantage of her better skills at fighting in the dark, is able to defeat the Waif.
As Arya, wounded, is running away, with her blood-covered hand she touches quite a few stone walls. This may be because she is weak from her wounds and needs to lean on the walls in her run. Or it could be that she is leaving a trace on purpose so as to lead the Waif where Arya thinks she can defeat her.
Does she leave the blood trace on purpose or not?