If its stopped buzzing I would be confident in saying the plug was at fault, maybe it wasn't in properly? OR. . . Squishy could just be going crazy and the buzzing was in her head!
I wouldn't worry too much though. Only 17% of house fires are cause by faulty outlets, where as 39% are caused by the faulty plug! And saying as the plug is now removed, you have removed the biggest hazzard! If you have someone you know who could take a look at it I would ask them. A sparky would charge you loads and I GUARANTEE they will not find anything! I would try one thing though, to put your mind at rest and cure my curiosity, just plug the plug into a different outlet, see if it buzz's!