GA probably asked her a few searching questions, to research the character she'd be playing, that SW couldn't answer or gave evasive answers to.
In the This Morning interview, GA does not look comfortable or happy. She mentions she listened to TSP in the car when driving her children around, i.e. not giving it her full attention, but still being hooked by the tale.
GA is quite subdued in the interview, she doesn't have rapport with SW, mainly just looks unsmilingly at SW when she is talking.
The only time she gets enthused is when she talks about the injustice that SW experienced, but that belief and enthusiasm came across to me as very much GA reflecting back on her own response to the book, rather than in connection with getting to know SW (RW) and establishing a much fuller understanding of the 'traumatic yet healing experiences' – which you would have expected if you spent time with the person it happened to.
At one point GA says "we had to tell the story", not "we had to tell their story" or "we had to share their experience".
My interpretation of it is that by the time GA was on the This Morning sofa she may have heard some rumours (at that point Penguin, and presumably the film company, had been approached by CH and The Observer team), or was just suspicious at not being able to probe SW (RW) very far, and was doing her best to just give a truthful account of why she wanted the role, and keep promoting the film, something she'd have been contracted to do. A tricky combination, she looks tense and uncomfortable about it.
Of course this is all retrospective fine-toothcombing, but noticed GA slightly narrows her eyes looking at SW on the word "truth", after saying this is the last thing anyone would do but that's the truth of what they did. It's like she's doubting it. GA also brings her hand over her mouth to touch her upper lip on the word "accuracy" and fidgets a bit when SW is talking.
Weirdly, SW manages to bring in the theme of identity and name mix up on Pamela/Gillian, and I thought it was a tiny bit disrespectful too, as in oh Tim just thought of another actress – rather than him being impressed it would be GA.