I knew what it was, I just did not know how quickly it was removed. Found some reading last night that pretty much said what you did...removed shortly after return, so I guess she had not been back all that long. This AM no evidence remained.
Earlier yesterday there had been a period of intense activity at the OB hive entrance, and when I uncovered it the Bees were simply frantic, and we could not find the queen. It was a few hours later that we looked again and saw her with the mating sign. She was easy to find,there was a mad circle all around her and over her. My wife had noticed a similar "ball" 2 days before and now we wonder if it is associated with return from the mating flights....this is way beyond the normal ring of attendants.
Also wondering if the frantic period we caught early yesterday afternoon was associated with her departure or return. Perhaps to allow her to hide in numbers while exiting?