No. Junes bedroom door was open since the killer was standing there. Across the landing by about 10 ft is the door to Sheila's room. A door that you don't even know was shut. But I will be generous and lets assume it was shut. The sound waves from the screaming and shooting only have to travel through one door across the landing.
June was not shot in the neck, she was shot in the collar bone area.
Then why insist she was asleep in the first place?
Bamber was standing over an asleep June & the bed when shooting her.
If June started screaming while still in bed, it would have to travel across the bedroom, through the door entrance (if open), across the corridor & through another wall.
If she started screaming when crawling, she was basically screaming into the floor. Again the scream would have to travel a long way. Through walls, doors & across corridors.
Either way, a badly injured June screaming is not exactly an alarm clock in a sleeping Sheila's ear.
You asked me what Sheila was doing while Bamber was committing the massacre. I said sleeping. It is better to deal in facts. There was a kitchen fight, so a very slim chance this noise travelled a long way upstairs through walls & woke Sheila. Not that it would deter Bamber.
Can you provide the photo of June.