Gettrick strangled Lena, as he tried to Sophie. Lena was v weak I reckon, he'd been starving her.
The house backed onto woodland, he carried Lena's body there, middle of the night, Websters all asleep, easy enough to drag the body up behind the shed and only need a few minutes to open the shed (key in padlock) let Sophie out and place Lena's body in.
The 3 hours? She may have taken a long time to find a petrol station and florists. Probably couldn't speak German and wouldn't want to ask anyone for directions.
Brig may have approved married quarters for Gettrick. The latent blackmail would have been Gettrick harping on about the fire and dead girl, maybe other girls Brig had in Iraq, the sudden pull on that blackmail being the recording and Sophie's appendicitis.
The DNA - Baptiste said the British Military had taken over the investigation. Still - bit foggy that point. Did Gettrick just hand Brig a sample from Alice?
Sophie knowing what Brig had done was a reference to Iraq that she'd been told (minus the 13 yr old).
Sophie's father - Baptiste said he made a mistake.
She doesn't want to see him because she's been told by Gettrick that her family didn't want to find her. She knows her mother's dead, she reacted to that as "Alice" - and is angry and confused.
By the time I post this we'll be many posts on!