Been reading a bit about this case over the weekend, and just exploring the evidence. I definitely have not reached a conclusion on her guilt or innocence, but I did find this which was interesting I thought...
Lucia de Berk - Wikipedia
Very similar situation in the Netherlands where a nurse was convicted of multiple murders on circumstantial evidence, the main point for the prosecution was a statistical argument that she had been present at the deaths. Similar to the Letby case. Eventually a group of scientists and statisticians debunked the prosecutions case and she was acquitted. a major miscarriage of justice.
Interestingly the main man who worked on the statistics and science to overturn that conviction - Richard Gill - is currently posting a lot in defence of Letby.
The Lucy Letby case – Richard Gill Statistics (gill1109.com)
It does seem like the Letby evidence is wholly circumstantial. Perhaps a better defence team could have countered the arguments of the prosecution - but the defence called no expert witnesses despite experts offering their services.