Oh, man, I'm flattered, but I don't understand her nuances nearly well enough to do a guide lol. I'm just more comfortable with it, if that makes any sense. A huge part of it is that even before development shut down, Hylian announced the character was pretty much finished and there were no more changes planned for them. I love the character a lot, so right about then I got used to the idea that we'd never get another patch that affected Icies. So even when it was announced that 3.6 would be the last patch, I wasn't too concerned over Icies. Since that happened I've really just been committed to accepting the character as they are, flaws and all. I'm getting really good at laughing dumb Nana stuff off because hey, I know what I signed up for.
So, no. I really wouldn't change anything about the way they are, period. That's just kinda how I am. A lot of people have their own complaints about Nana's AI and would probably agree with you on some proposed changes, but that sort of discussion happens more in the discord nowadays (like most discussion about PM, sigh), which I can link you to if you like.
And Nana does periodically do attacks like that when she's AI controlled, which they way I see it can be irritating or beneficial. It's a coin toss that I try to be prepared to accept. Like that GRSmash video, yeah. Actually, just the other night something amazing like that happened. I was sparring against a Falcon player, and we were on the Smashville platform above the blast zone. He had one stock left, I had two. He killed me off the top, but only hit Popo. When he dropped through the platform, Nana dropped with him and spiked him and won me the game. ^_^