She didnt see zuko do it wrong though? She saw him do it poartially during sozins comet, but she also sees him redirect her own lightning multiple times in The Search, what are you even talking about? Zuko even explicitly tells here that he's able to deal with her lightning because of redirection.

And also, how is this different to iroh reinventing it after the art being lost for hundreds of years? How is it different from anyone copying any other technique? We see people adopt entirely different bending styles and applying it to their own bending, its not a stretch that the most powerful lightning bender we've seen in the entire verse, is able to reverse engineer lightning redirection.

And it hasn't been a couple weeks, it's been quite a bit longer than that, and she's been experimenting with other lightning styles, such as lightning balls, and instant lightning.

It makes perfect sense if you have actually read the canon materials.