I don't know if this is a possibility, but we tried the "Bark Off" system one time (same principle, audible, no shock or spray) and quit using it after two days.
I had reservations because we have five Yorkies and only 1 is a barker, but if ANY of them barked then it would go off effectively penalizing the group.
The barker seemed to be immune to what noise is created (undetectable to human ears) but it sent two of our others into a bad place.
They urinated and defecated where ever they were and stayed clear of that side of the room and wouldn't go near it.
After day two, I disposed of it because of the effects it had on the others.
She may have gotten close and the sound has scared her where she associates it with the outdoors (our two that had the issue were both and still are very sensitive to loud noises and are the first to hide during a thunderstorm--you could equate them to being more timid than the rest).
Don't know for certain, but you might consider talking to a professional trainer who might know more. This was just our experience.