Is it the case that the two ambulances were called to the scene and arrived at the same time as the second group of firearms officers because the raid team was preparing to force an entry into the farmhouse with the intention of shooting dead Sheila if the opportunity arose? Were the police instructed to shoot to wound Sheila, rather than shoot to kill her, and was that the reason why only one ambulance was required at the house immediately, with another one on standby?
Was the mysterious "Dr Harris" present at the scene, at this time?
There could be some mileage in this proposition...