Plenty of corrupt conduct doesn't quite meet the criminal standard. It's one reason bodies like ICAC exist. In this instance, it seems like Berejiklian should have declared her conflict and recused herself from dealing with these grants. But did her relationship actually change how she acted on them? That's harder to prove even if it was the case.

Edit: this page has info on the elements that constitute criminal misconduct

Edit2: oh yeah, ICAC also has coercive powers that allow it to get evidence that would be inadmissible in court. There's probably a bunch of that here.