LOL She's adorable! I can also see why it's hard not to reinforce it. My two are generally quiet, but sometimes do that when they get really excited. Lilo does exactly like Ponyo while Rocky does that + a cute little howl. Everybody can't help but find it cute... and they know it.
I suppose the way to change it is to change our reactions. We try to stop what we're doing and ignore them until they've calmed down. For example, if it's at the beginning of a training session with treats, I walk away until they stop. In the situation in your video, it's a bit hard because she does go quiet when you come back. In my case, they do it in front of me so I ignore them and don't put the food bowls down until they've calmed down. I think if she stops getting attention when barking, it shouldn't get worse.
In our case, it's particularly bad with the friend we live with right now. They go crazy around him and he just reinforces it. He even barks back at them to excite them even more... no matter how many times we've told him not to do that/to ignore them. It was cute at first, but it's really getting out of control. lol