difficult distinction. but I have never been one to turn my back to a good challenge.
"She is in the world" is pretty simple. no connotation about it. She is simple a person, living on the planet earth. One living being , there. No other implications.
The other phrase however, I would say does have some connotations. To say you are "of the world" implies that you are "worldy" or partaking in very human things. Worldy could mean you like money or fast cars. You are very impressed by what the culture dictates. You are essentially, governed by the world of humans