In my opinion, the best thing you can do is work on her recall. Using very tempting treats such as chopped up hotdogs, call her constantly and treat her with a treat as well as praising her excitedly every time she comes. If she loves to chase a ball, you can toss her a ball too when she comes as reward (my golden Tommy particularly loves that reward!). Once she starts associating wonderful things with coming and gets eager to come when called, you can simply call her as soon as she starts barking and she should stop and run to you, thus getting incredible reward. This will serve to focus her attention on you more and will diminish her boredom and barking.

I personally wouldn't agree with a startle technique like the penny can or spraying water simply because in my personal experience, I have found it ends up making the dog jumpy and more nervous. I think it risks giving a negative association to the thing she is barking at. I say this partly because we used to clap or make a startling noise when Tasha was younger and we caught her getting into something like the trash. Now, when a stick breaks or a popping noise happens, she goes slinking off looking guilty or frightened. I regret very much that we ever did that method instead of simply calling her away and rewarding her for coming.

Good luck.