There are so many charges that can be made and I hope the prosecutor makes them all. Even without the alcohol, you have reckless endangerment. You turn the engines off. Now we can speculate based on his history that she was drinking. If he supplied her with alcohol another charge there plus makes him have responsibility for her actions. Why she dove in I guess will come out in the case.
I would guess he'll win the criminal case or plead it way down. But that brings to the civil case and I think if his insurer doesn't settle with the victim before that case, he's very likely to lose.
Obviously we don't know all the facts. But he was definitely drunk and operating a boat. .09 four hours later is evidence enough unless he claims he had a drink while in custody.
As to doubting whether a zero reading would have prevented the accident, that's saying you believe he was too stupid to turn the engines off sober and too stupid to allow a passenger to dive in with the boat under power.
I certainly see some fault with the victim, but if she was served alcohol on the boat, then the percentage for which she's held accountable drops rapidly. I would also say the fact he is a bar owner and his profession as fighting DUI's could very much work against him.
Which brings us to where the alcohol came from. If it came from the bar, then add some more trouble. Means he was serving her as bar owner, an extension of the bar. Not the case if he bought it at retail somewhere.
Sad they couldn't find her arm. Painful to think about. However, I did work with a young girl who lost most of an arm and she adapted incredibly well.