If she wanted to rely on the fact there was no proven crime, she shouldn't have conceded that the insulin babies were murdered by someone (but not by her).
From her statements and cross-examination, it seems she has a very lax attitude to medical documentation (not completing babies' drug charts until the next day, inputting notes retrospectively, making countless favourable errors on dates, times and sequences of events that were contradicted by phone records, witnesses. etc), and that blasé approach seems to have extended to her having formally agreed a large amount of evidence put forward by the prosecution (including witness testimony from the babies' parents and medical staff) which she then sought to dispute under cross-examination. What did she think all that paperwork the prosecution sent her was for? Didn't her defence team explain what it meant? She agreed that reams of stuff could be read out to the jury as mutually accepted facts, so it was and the jury heard it in that context, and then much later she turns round under cross-examination and says that actually, she doesn't agree with huge chunks of what had been presented as agreed - well, the jury can't unhear it at that point, can they? Plus it looks suspicious that she agreed witness statements before but then she's changed her mind now she's realised which bits suddenly look more damning (e.g. after phone records and other documentation have confirmed timelines that were previously presented as different or more vague).
She also sought to add extra key details to her original police statements on cross-examination, which obviously doesn't look great to a jury if she's seeking to rely on these details as her defence but only thought to add them in later. She had years to get this stuff right - why on earth was ensuring her defence was 100% factually accurate not her utmost priority?
There were also several instances where she tried to point out other people's involvement in specific events, but then refused to name the colleagues she was talking about, as if she were being accused of spreading a high school rumour as opposed to being tried for multiple murders. Obviously the prosecution suggested that she knew if she named names, those people would dispute what she had said, so her repeated vagueness made her look like a liar, regardless of whether she was telling the truth or not.
Sure, it could be argued that if she's innocent, perhaps she genuinely didn't believe she'd ever be convicted, but this investigation had been going on for years and she'd seen the evidence against her - I can't imagine being wrongly accused of such serious crimes yet approaching my defence in such a vague and haphazard way, as if I'm not that bothered whether I get convicted or not.
If you're innocent, you don't just concede "yes, if you say so" when witnesses are supposedly lying about you, and you don't just agree that their made-up and damning version of events can be presented to the jury as the agreed truth - you say "no, that's not what happened" every time you're asked if you agree with it. You don't just say "yeah, whatever" and then wonder what went wrong.