She probably smelled something. An evil rabbit or something. ;) Don't discount the amount of information dogs intake thru there nostrils. Their sense of smell is way beyond anything we experience and it plays a huge roll in how they interact with their environment.
Something's up. Her ruckus may have chased it (him?) away. I take this kind of thing seriously, though try not to get hysterical about it. Remain calm. You're the boss, and you set the tone.
There was something...unseen to the human! I can tell by Wynn's bark what's going on. he has a special "alert" bark when something "not right" is going on. I listen to him because it's been people in our yard or things like that!
Maybe it was a Fairy! Corgis are known for this...I don't really call it a behavior but they really are smart and something was "off" or making her suspicious!
A German shepherd made a believer of me...to this day I suspect she actually did sense some sort of spirit.
Ahem. Assuming such things exist....