The appearance and demeanour of a defendant is utterly irrelevant if evidence for their crimes does not meet the threshold of beyond reasonable doubt, as opposed to the balance of probabilities, which applies in civil / family courts but not in criminal courts for very good reason.
It is tedious and lazy when this trope gets trotted out. The only reason this case is where it is, is because medical practitioners and experts, who probably thought, like many of us here, that the case wouldn't have come to court without very solid medical evidence, started hearing about air down NG tubes and splinting of diaphragms, violence committed to livers in frankly improbable circumstances leaving no other trace, dubious methods of introducing insulin into babies etc etc and went "hang on a minute, by no stretch does this chime with our years of practise and experience nor precedents from other similar cases." And they started making "noise" as Lady T put it because if these things are allowed to stand without rigorous scrutiny, it makes a mockery of both science and justice.
As the management of the whole case was also scrutinised it began to look like a really shit episode of Life on Mars, a return to policing practise that had been identified as central to other MoJs.
If anything, partly based on personal experience, Lucy's status as middle class white female might even have counted against her in terms of a subconscious effort to emphasise that these things are no guarantee of innocence - nice middle class people can be monsters too. Women who fight back against the system strongly are often doubled down on, the first line of attack is often to cast doubt on their mental health, or their morals. I've said before,the lack of any psychological reports or people who knew her coming forward with salacious reminiscences to the tabloids is extremely unusual in such a high profile case as this.
But the bottom line is that a vast number of people from all walks of life approached this case believing it must have merit until the reporting of the medical evidence made them go hang on, that's not possible. For me that's where it stops and starts.
There is new opinion from another expert today about the validity of the air embolism theory, based on what was NOT observed at post mortem. Very interesting indeed, and it has certainly upset Dewi Evans.