In this picture, taken long after what Henri Cartier-Bresson, the greatest snapshot photographer who ever lived, called the decisive moment, Roo has just gotten through running a fake charge on Ranger the Buffalo. She ran straight at him and then broke left. Ranger, as you can see, was inconvenienced. This is why I call this shot Thank God for barbed wire.
If the wire wasn't there, would Roo have tried something as idiotic as this? Ranger is a friendly buffalo. I don't know if he's as friendly as the famous Andy of Catalina Island, who used to roam around the road between the airport and town and let tourists stop and pet him, but Ranger is a pretty friendly old boy. At least with humans. Wolves he probably doesn't think as highly of, especially blonde ones.
Would Roo try a kamikaze move like charging a buffalo if there wasn't any barbed wire between her and certain death? Does she know she's only getting away with it because Ranger can't get to her? My guess is yes.