Great post!
SH is a survivor and mentally stronger than NM without a doubt. As a child, she would have gradually learned to be charming and agreeable to fit in with a family and quickly realized that negative/rebellious behaviour could mean being sent on. As a survivor, shutting down emotions especially when things get too tough to handle is a great gift. People who have difficulties with this technique will usually end up resorting to heavy drug use or alcohol to dull the emotional pain, so I take my hat off to SH for her mental strength and resilience.
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There are two things that bother me about NM's story about his relationship with SH and his constant rebuttals to suggestions she was involved in the
'before, during or after' (his words).
Firstly, NM claims SH would have given him up to the police if she knew about the plan or subsequent hiding and disposal of the body. I don't believe this for a second. SH imo, would have immense difficulties in contacting the police for even a minor matter. SH didn't contact police after being physically assaulted on many occasions by NM. SH would have problems with authority which is extremely common for people who've been in care. I believe NM to be the opposite, and hold the police and authority in high regard even if he's a bit 'dodgy' himself. NM was confident SH wouldn't do it under any circumstances!
Secondly, NM says he brought SH to Becky's house
because he always took her with him. SH was his best friend, confidante and lover. Whatever designs he had on Becky he would share with SH. There are people who have a double life, I don't think this the case with NM, he has one life and it's with SH. NM would share his dreams, fantasies, fears and disappointments while SH had the role of consoling and cheering him up.
So in saying all that

, I believe SH knew about the plan and accepted NM's reasoning however bizarre. If it were to 'teach Becky a lesson' or take her to their attic for 'some fun', she'd be on board with that. NM putting the plan into action meant Becky had to die eventually and NM would be able to rationalize that also. SH probably didn't consider Becky had to die or didn't care. So with that being said, SH was part of the plan even if it was just approval of NM going ahead with it.
I think the argument they had was about the dismemberment of the body. I don't believe SH was agreeable to it and for once put up a fight. This is where I believe her when she says Becky didn't deserve that.........
the dismemberment.
If SH is found guilty on
perverting the course of justice, conspiracy to commit false imprisonment and preventing lawful burial of Becky, I think she will receive a very minimal sentence due to her history and the controlling nature of the relationship with NM since she was 15 yrs old.
SH could get off scot-free too. I say this because I believe SH knew enough to be complicit.
If SH had a larger role as in aiding NM with subduing Becky, helping with the cutting up/packaging of the body or worse, actually caused Becky to die by suffocation, well that's something she has to live with but she will probably manage by compartmentalizing, another useful trait used by survivors.
JMO