Unless I am mistaken, these sentence structures come from English’s Germanic roots, in which sentences are arranged very differently from the way we use them now.

Or I could be totally wrong and it’s just a commonly accepted grammatical error, like “ain’t,” and everybody simply uses it because it flows.

In fact, if you’re old school, you could say, “Is not she nice?”

Someone said that you should put “not’ after “she” but that gives it a totally different meaning. What you’re asking is not even a really a question. It’s more rhetorical. “Isn’t she nice?” asks for a “yes” as a response. therefore, “Is not she nice?” would be ok. I wouldn’t use it though. That’s the nice thing about English. It’s a mutt. Mutts are ugly, but can be quite useful.

is not it is

not is as

not as is…