Saying she was the only one on shift is only relevant if you know for certain there was a murder and you're just trying to work out who had opportunity. If they could prove a deliberate air embolism was caused in both babies, it's very damming that she was with them just before, and that she was the only person present both times.
But an air embolism could be accidental, or equipment failure, bad placement etc and we don't know conclusively that it was air embolism. Rather doctors at the time found no definitive cause and if those were the only two incidents in 2015, no one would be talking about them further. As more and more (but still only a handful) deaths happened, more scrutiny was applied, and more effort to find any common cause. It does seem the air embolism only became a theory after they began considering foul play.
It's also very difficult to determine insulin overdose. It doesn't seem like anyone suspected that at the time in the case of the first child, this seems to be a theory that again appeared after they began looking for ways it could have been murder. If insulin overdose is difficult or impossible to determine with certainty, and multiple reviews closer to the time didn't suggest it - how much confidence can we have in the independent experts who say it was definitely murder by insulin overdose when they most certainly were aware they were being consulted over a suspected murder?
If you dug out my whole Facebook search history, some of the searches I'd remember, some of them I would not, but I'd believe the Facebook search history if it said I searched for them. It sounded like a specific answer to a specific question about a specific search at a specific time. Surely she was asked multiple times about searches for different people at different times, it doesn't seem to be suggesting she consistently claimed to have no memory of any of it.