Oh wow! How scary, that would terrify me! Not to mention the chooks.I am only guessing. There are always foxes around my place and it was getting towards dusk (which is why I was out there). It didn't seem like her normal rushing around so I assume she was spooked.
It was very like Maggie (also a big gal) who once did a vertical lift off to avoid a fox that snuck up on her (and me).