I must admit, I have been basing my assumptions of SH being totally involved in all of it from the video interviews showing her obvious (sorry!) hatred of Becky, as well as circumstantial evidence - her locations at the time of all of these events (being in the house when Becky was killed, going shopping with NM for supplies, living in the house with the body, and being at the house when the men came round re transporting the body parts. And of course the text messages re kidnapping of girls. I do agree with what you are saying - that the average person may not think as in depth as those with an interest/knowledge of crime and forensics - so some things may not have stood out at the time.
That said, IF she was totally innocent, then she must have been extremely gullible, unquestioning and totally wrapped up in her own world .... or perhaps suspected what had happened, but hated Becky so much that she was happy to keep quiet and just bury her head in the sand.
Is it really possible for ALL of the following things to have happened though, and not one single one of them cause alarm bells to her?
* NM parks his car a different way to usual - saying he was going to wash the car, but never did. (It was raining that day)
* Becky goes missing and they were the last people to see her - remember that SH didn't actually witness Becky leave the house.
* SH doesn't hear a struggle, which appears to have occurred across at least 2 rooms, and ended with the death of a person.
* Becky goes missing and suddenly SH is barred from going into her bathroom for goodness knows how many days.
* SH doesn't hear the sound of electric sawing in the middle of the night .... or hears it but isn't suspicious.
* NM develops a sudden interest in deep cleaning one room of their filthy house.
* A number of items of clothing, bath mats and the shower curtain go missing from her home.
* NM needs a bunch of blokes to move some suspicious packages from their house (bearing in mind, nobody has been to the house to deliver stolen goods or drugs, and he hasn't apparently been anywhere to collect them).
Okay, I can almost believe one or two of these events might pass without notice/interest, but ALL of them? Really? I'd say at best she knew what had happened, but did nothing about it because it suited her that Becky was no longer around.
She certainly played a part when the police wanted to come round to search their house and she suddenly developed a need to visit her estranged family for the first time in years. I don't believe that was pure coincidence.
