Birthday Angel?

So we've been approaching 4 years old in this house... and recently she has been showing her strong-willedness quite openly and often. But... something has changed this week. She has been very cooperative, easily saying she's sorry for minor things, but correcting herself when asked to and in a general good mood. Now, I'm not sure that it's because she will be four (tomorrow), but rather that her birthday (read: party) is coming up... I'm not sure, but I have a hunch. Anyone else ever experience this phenomena??