As was mentioned, 나비 can mean both "butterfly" and "cat".
나비 as "butterfly" is a common word, while 나비 as "cat" is not as universal ("cat" is 고양이 first and foremost).
And yes, cats have been traditionally associated with superstitions, so people tended not to use it in their names.
But in modern times, people don't give a whit about such superstitions. There's nothing wrong with cats.
So if you want "butterfly" for your name, I would say 나비 is a beautiful name.
If you do search on 김나비 or 박나비, you see a bunch of people with these names. It seems already popular.
To me it is as good a name as any. If you like it, just go for it. There is nothing to worry about in my opinion.