I am not really sure Jez .... In a trial, witness testimony is considered evidence, but since TLM and MR were co-accused, and much of the case against MR hinges on her testimony, it seems that the judge will caution the jurors about relying too much on TLM's testimony - that is why the earlier interviews with LE and her criminal records were allowed in - to show the jurors what type of person she is. They can choose to believe all or part of her testimony, or none at all. The LE interviews tho were not under oath (like she cares lol) so they aren't "evidence" but just to show how she changes the story and her behaviour at will. They do not have to believe that MR told her to abduct a child, that any of their "conversations" took place, that he raped the child (assuming no proof is presented). She just isn"t credible, and the judge needs to make sure the jury knows that just in case there is an appeal.
The other part of it is that the jury will be deciding on a finding - Murder 1, Murder 2 or manslaughter depending upon what they feel was the extent of MR's culpability. So it is important that they fully understand that TLM is not credible ... this isn't really a case of guilty or not guilty - the jury has options.
The defence will try to show that TLM is violent, coniving and volatile - and that her mindset on the day TS was abducted was to kill someone - hence the production of the disgusting letters, journal, Facebook, and the music that she was listening to at the time - which the defence will say she used to pump herself up.
The unfortunate part about relying on tweets and news reports is that we cannot hear the background activities - what the judge says to the jurors or to the lawyers ... a lot of the techie stuff is glossed over.
As for her prior knowledge of the discovery materials, much of what was presented in her case will be the same as in MR's case, and the judge will make sure too that the jury is aware of her being privy to the materials which gives her the possible ability to tailor her testimony to line up with the evidence. After all, she lied at her own sentencing, profusely apologized to the family and didn't come clean about the extent of her participation. The family has suffered more and longer because of her deceit.
There are no words to describe how evil she is. I hope she never gets out.
JMO