It's not as though her runes have ever truly let her down before. She was the one who made them after all. But if the equation isn't right...

Neko comes to a halt at the edge of the torch line, her fur standing on end when she realizes that her other frequent hiding spot is well outside of the safe zone now. She wrings her tails in her hands for only a second or two before searching for an empty building to break into.

And it does mean there are fresh tracks in the snow when Hermione comes that way.