When screenwriters write films about children or the mentally challenged, the difficulty seems to be the same thing - the "aww" factor takes over. Both end up being mere entertainments for us. This completely dehumanizes them and makes them *characters*, not people. That is the trouble with this movie. The dialogue is too cutesy and saccharine to be taken seriously, and although the main character demands we treat her as a person, the movie fails to see that it isn't treating her like one, either.
I'm not sure whether it makes it better or worse that every character was written like this. They are all clearly there just to serve the script's purpose, not because they actually are characters in and of themselves. Even Diane Keaton, who is a very interesting actress, can't save this film. She's forced to play a character who, from the evidence, is quite possibly bipolar... or at the very least emotionally unstable. She switches emotions faster than [insert punchline here of whatever you want].
This movie is a collection of nonsensical sappy scenes and is at the very least mildly offensive in its refusal to explore Carla's actual personality. Instead it just shows us a bunch of cute "aww" moments that are ineffective if we don't care about the people we're watching. It might possibly rate half a star, but I've decided to be gracious and give it a whole one.