I think you may have misunderstood the effect hitting the water tendril with the staff had. I used the word 'wrap' in the same way you may 'wrap' a baseball bat round someone's head, as in to hit something so hard the weapon bends at the point of contact and crashes around. That's why I then said the tendril was coming in from behind her (because it had about six feet of extra water to work with, that extra water wrapped around the staff and crashed into her back.)

It isn't literally wrapping around the staff like a whip.