It is how I feel.
Sheila was not shooting when Neville made his call. Neville would not have had the 5 - 10 minutes to make two calls.
So if no shots were being fired Neville & June would have calmed her down. Or wrestled the gun away. Certainly not phoned Jeremy at 3.26.
Neville certainly would not have left Sheila alone in another room with a gun, while he went downstairs to phone Jeremy.