Dave,
I hope that works out for you. I would think as long as they can't prove you did it and she didn't witness you shooting it you are O.K. (As you didn't anyway) Are they doing an autopsy? Animals do just die at some point for God's sake! And herons do have some predators!
Keep in mind I think it's technically illegal to harass them with a gun even if you aren't actually shooting them. So don't volunteer that.
Here are some pics that may help. I really think the stakes and line are very effective 99 percent of the time and they are perfectly legal. In fact several federal publications suggest it. They also frustrate geese, but I did get a morning dove get his wing caught in the mono once. I was able to release him though.
Here I've rigged up more than one line on the belt feeder side of the pier to prevent a heron from taking advantage of the situation where small fry are concentrated.
